現在我們已經了解了字符串的基礎知識，讓我們開始思考我們可以使用內置方法對字符串執行哪些有用的操作，例如查找文本字符串的長度，連接和拆分字符串 ，將字符串中的一個字符替換為另一個字符，等等。
| 先備知識: | 基礎的電腦素養、基本的HTML和CSS、以及清楚什麼是JavaScript。 |
|---|---|
| 目標: | 了解字串是物件，學習使用一些能夠應用這些字串的基礎方法。 |
我們曾經說過，現在我們重申一遍—在javascript中，一切東西都可以被當作物件。例如我們創建一個字串。
var string = 'This is my string';
你的變數成為一個字串的實體物件，因此它將有許多性質(properties)與功能(methods)可以使用。
你的變數成為一個字串的實體物件，因此它將有許多性質(properties)與功能(methods)可以使用。你可以到 {{jsxref("String")}} 物件頁面的左方列表查看這些性質與功能!
好的，在你腦袋燒壞之前先別擔心！在這趟學習旅程中，關於這些大部分對於現在的你其實還不需要知道。不過有一些你可能會經常使用，我們將在這裡介紹。
Let's enter some examples into a fresh console. We've provided one below (you can also open this console in a separate tab or window, or use the browser developer console if you'd prefer).
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>JavaScript console</title>
<style>
* {
box-sizing: border-box;
}
html {
background-color: #0C323D;
color: #809089;
font-family: monospace;
}
body {
max-width: 700px;
}
p {
margin: 0;
width: 1%;
padding: 0 1%;
font-size: 16px;
line-height: 1.5;
float: left;
}
.input p {
margin-right: 1%;
}
.output p {
width: 100%;
}
.input input {
width: 96%;
float: left;
border: none;
font-size: 16px;
line-height: 1.5;
font-family: monospace;
padding: 0;
background: #0C323D;
color: #809089;
}
div {
clear: both;
}
</style>
</head>
<body>
</body>
<script>
var geval = eval;
function createInput() {
var inputDiv = document.createElement('div');
var inputPara = document.createElement('p');
var inputForm = document.createElement('input');
inputDiv.setAttribute('class', 'input');
inputPara.textContent = '>';
inputDiv.appendChild(inputPara);
inputDiv.appendChild(inputForm);
document.body.appendChild(inputDiv);
inputForm.addEventListener('change', executeCode);
}
function executeCode(e) {
try {
var result = geval(e.target.value);
} catch(e) {
var result = 'error — ' + e.message;
}
var outputDiv = document.createElement('div');
var outputPara = document.createElement('p');
outputDiv.setAttribute('class','output');
outputPara.textContent = 'Result: ' + result;
outputDiv.appendChild(outputPara);
document.body.appendChild(outputDiv);
e.target.disabled = true;
e.target.parentNode.style.opacity = '0.5';
createInput()
}
createInput();
</script>
</html>
{{ EmbedLiveSample('Hidden_code', '100%', 300, "", "", "hide-codepen-jsfiddle") }}
這很簡單，你可以用 {{jsxref("String.prototype.length", "length")}} 屬性。試著輸入下面幾行：
var browserType = 'mozilla'; browserType.length;
結果應該會回傳數字7，因為 "mozilla" 字元長度是7。 這在很多狀況下很好用，舉例來說：你會想知道序列的長度，這樣才能將這些序列按照長度排序，或是讓使用者知道他們輸入的名稱是否太長。
On a related note, you can return any character inside a string by using square bracket notation — this means you include square brackets ([]) on the end of your variable name. Inside the square brackets you include the number of the character you want to return, so for example to retrieve the first letter you'd do this:
browserType[0];
記得電腦計數從0開始，不是1！ 如果要在任何一個字串中取得最後一個字元，我們可以使用以下程式碼，結合了取得字元的技巧和上面學過的長度屬性：
browserType[browserType.length-1];
"mozilla" 這個詞的長度是7，但因為電腦是從0開始計數，所以最後一個位置是6，因此我們會將 length-1 。你也可以試試用這個方法找各序列的第一個字母，並將這些序列按字母順序排好 。
browserType.indexOf('zilla');
結果會傳回2，因為子字串 "zilla" 在 "mozilla" 中是從位置2開始的。（依然要記得電腦計數是從0開始）。這個方法可以用篩選字串，舉例來說：我們有一串網址的清單，而我們只想印出那些包含 "mozilla" 的網址。browserType.indexOf('vanilla');
This should give you a result of -1 — this is returned when the substring, in this case 'vanilla', is not found in the main string.if(browserType.indexOf('mozilla') !== -1) {
// do stuff with the string
}
browserType.slice(0,3);This returns "moz" — the first parameter is the character position to start extracting at, and the second parameter is the character position after the last one to be extracted. So the slice happens from the first position, up to, but not including, the last position. In this example, since the starting index is 0, the second parameter is equal to the length of the string being returned.
browserType.slice(2);This returns "zilla" — this is because the character position of 2 is the letter z, and because you didn't include a second parameter, the substring that was returned was all of the remaining characters in the string.
Note: The second parameter of slice() is optional: if you don't include it, the slice ends at the end of the original string. There are other options too; study the {{jsxref("String.prototype.slice()", "slice()")}} page to see what else you can find out.
The string methods {{jsxref("String.prototype.toLowerCase()", "toLowerCase()")}} and {{jsxref("String.prototype.toUpperCase()", "toUpperCase()")}} take a string and convert all the characters to lower- or uppercase, respectively. This can be useful for example if you want to normalize all user-entered data before storing it in a database.
Let's try entering the following lines to see what happens:
var radData = 'My NaMe Is MuD'; radData.toLowerCase(); radData.toUpperCase();
You can replace one substring inside a string with another substring using the {{jsxref("String.prototype.replace()", "replace()")}} method. This works very simply at a basic level, although there are some advanced things you can do with it that we won't go into yet.
It takes two parameters — the string you want to replace, and the string you want to replace it with. Try this example:
browserType.replace('moz','van');
Note that to actually get the updated value reflected in the browserType variable in a real program, you'd have to set the variable value to be the result of the operation; it doesn't just update the substring value automatically. So you'd have to actually write this: browserType = browserType.replace('moz','van');
In this section we'll get you to try your hand at writing some string manipulation code. In each exercise below, we have an array of strings, and a loop that processes each value in the array and displays it in a bulleted list. You don't need to understand arrays or loops right now — these will be explained in future articles. All you need to do in each case is write the code that will output the strings in the format that we want them in.
Each example comes with a "Reset" button, which you can use to reset the code if you make a mistake and can't get it working again, and a "Show solution" button you can press to see a potential answer if you get really stuck.
In the first exercise we'll start you off simple — we have an array of greeting card messages, but we want to sort them to list just the Christmas messages. We want you to fill in a conditional test inside the if( ... ) structure, to test each string and only print it in the list if it is a Christmas message.
<h2>Live output</h2>
<div class="output" style="min-height: 125px;">
<ul>
</ul>
</div>
<h2>Editable code</h2>
<p class="a11y-label">Press Esc to move focus away from the code area (Tab inserts a tab character).</p>
<textarea id="code" class="playable-code" style="height: 290px; width: 95%">
var list = document.querySelector('.output ul');
list.innerHTML = '';
var greetings = ['Happy Birthday!',
'Merry Christmas my love',
'A happy Christmas to all the family',
'You\'re all I want for Christmas',
'Get well soon'];
for (var i = 0; i < greetings.length; i++) {
var input = greetings[i];
// Your conditional test needs to go inside the parentheses
// in the line below, replacing what's currently there
if (greetings[i]) {
var result = input;
var listItem = document.createElement('li');
listItem.textContent = result;
list.appendChild(listItem);
}
}
</textarea>
<div class="playable-buttons">
<input id="reset" type="button" value="Reset">
<input id="solution" type="button" value="Show solution">
</div>
html {
font-family: sans-serif;
}
h2 {
font-size: 16px;
}
.a11y-label {
margin: 0;
text-align: right;
font-size: 0.7rem;
width: 98%;
}
body {
margin: 10px;
background: #f5f9fa;
}
var textarea = document.getElementById('code');
var reset = document.getElementById('reset');
var solution = document.getElementById('solution');
var code = textarea.value;
var userEntry = textarea.value;
function updateCode() {
eval(textarea.value);
}
reset.addEventListener('click', function() {
textarea.value = code;
userEntry = textarea.value;
solutionEntry = jsSolution;
solution.value = 'Show solution';
updateCode();
});
solution.addEventListener('click', function() {
if(solution.value === 'Show solution') {
textarea.value = solutionEntry;
solution.value = 'Hide solution';
} else {
textarea.value = userEntry;
solution.value = 'Show solution';
}
updateCode();
});
var jsSolution = 'var list = document.querySelector(\'.output ul\');\nlist.innerHTML = \'\';\nvar greetings = [\'Happy Birthday!\',\n \'Merry Christmas my love\',\n \'A happy Christmas to all the family\',\n \'You\\\'re all I want for Christmas\',\n \'Get well soon\'];\n\nfor(var i = 0; i < greetings.length; i++) {\n var input = greetings[i];\n if(greetings[i].indexOf(\'Christmas\') !== -1) {\n var result = input;\n var listItem = document.createElement(\'li\');\n listItem.textContent = result;\n list.appendChild(listItem);\n }\n}';
var solutionEntry = jsSolution;
textarea.addEventListener('input', updateCode);
window.addEventListener('load', updateCode);
// stop tab key tabbing out of textarea and
// make it write a tab at the caret position instead
textarea.onkeydown = function(e){
if (e.keyCode === 9) {
e.preventDefault();
insertAtCaret('\t');
}
if (e.keyCode === 27) {
textarea.blur();
}
};
function insertAtCaret(text) {
var scrollPos = textarea.scrollTop;
var caretPos = textarea.selectionStart;
var front = (textarea.value).substring(0, caretPos);
var back = (textarea.value).substring(textarea.selectionEnd, textarea.value.length);
textarea.value = front + text + back;
caretPos = caretPos + text.length;
textarea.selectionStart = caretPos;
textarea.selectionEnd = caretPos;
textarea.focus();
textarea.scrollTop = scrollPos;
}
// Update the saved userCode every time the user updates the text area code
textarea.onkeyup = function(){
// We only want to save the state when the user code is being shown,
// not the solution, so that solution is not saved over the user code
if(solution.value === 'Show solution') {
userEntry = textarea.value;
} else {
solutionEntry = textarea.value;
}
updateCode();
};
{{ EmbedLiveSample('Playable_code', '100%', 590, "", "", "hide-codepen-jsfiddle") }}
In this exercise we have the names of cities in the United Kingdom, but the capitalization is all messed up. We want you to change them so that they are all lower case, except for a capital first letter. A good way to do this is to:
input variable to lower case and store it in a new variable.result variable to equal to the final result, not the input.Note: A hint — the parameters of the string methods don't have to be string literals; they can also be variables, or even variables with a method being invoked on them.
<h2>Live output</h2>
<div class="output" style="min-height: 125px;">
<ul>
</ul>
</div>
<h2>Editable code</h2>
<p class="a11y-label">Press Esc to move focus away from the code area (Tab inserts a tab character).</p>
<textarea id="code" class="playable-code" style="height: 250px; width: 95%">
var list = document.querySelector('.output ul');
list.innerHTML = '';
var cities = ['lonDon', 'ManCHESTer', 'BiRmiNGHAM', 'liVERpoOL'];
for(var i = 0; i < cities.length; i++) {
var input = cities[i];
// write your code just below here
var result = input;
var listItem = document.createElement('li');
listItem.textContent = result;
list.appendChild(listItem);
}
</textarea>
<div class="playable-buttons">
<input id="reset" type="button" value="Reset">
<input id="solution" type="button" value="Show solution">
</div>
html {
font-family: sans-serif;
}
h2 {
font-size: 16px;
}
.a11y-label {
margin: 0;
text-align: right;
font-size: 0.7rem;
width: 98%;
}
body {
margin: 10px;
background: #f5f9fa;
}
var textarea = document.getElementById('code');
var reset = document.getElementById('reset');
var solution = document.getElementById('solution');
var code = textarea.value;
var userEntry = textarea.value;
function updateCode() {
eval(textarea.value);
}
reset.addEventListener('click', function() {
textarea.value = code;
userEntry = textarea.value;
solutionEntry = jsSolution;
solution.value = 'Show solution';
updateCode();
});
solution.addEventListener('click', function() {
if(solution.value === 'Show solution') {
textarea.value = solutionEntry;
solution.value = 'Hide solution';
} else {
textarea.value = userEntry;
solution.value = 'Show solution';
}
updateCode();
});
var jsSolution = 'var list = document.querySelector(\'.output ul\');\nlist.innerHTML = \'\';\nvar cities = [\'lonDon\', \'ManCHESTer\', \'BiRmiNGHAM\', \'liVERpoOL\'];\n\nfor(var i = 0; i < cities.length; i++) {\n var input = cities[i];\n var lower = input.toLowerCase();\n var firstLetter = lower.slice(0,1);\n var capitalized = lower.replace(firstLetter,firstLetter.toUpperCase());\n var result = capitalized;\n var listItem = document.createElement(\'li\');\n listItem.textContent = result;\n list.appendChild(listItem);\n\n}';
var solutionEntry = jsSolution;
textarea.addEventListener('input', updateCode);
window.addEventListener('load', updateCode);
// stop tab key tabbing out of textarea and
// make it write a tab at the caret position instead
textarea.onkeydown = function(e){
if (e.keyCode === 9) {
e.preventDefault();
insertAtCaret('\t');
}
if (e.keyCode === 27) {
textarea.blur();
}
};
function insertAtCaret(text) {
var scrollPos = textarea.scrollTop;
var caretPos = textarea.selectionStart;
var front = (textarea.value).substring(0, caretPos);
var back = (textarea.value).substring(textarea.selectionEnd, textarea.value.length);
textarea.value = front + text + back;
caretPos = caretPos + text.length;
textarea.selectionStart = caretPos;
textarea.selectionEnd = caretPos;
textarea.focus();
textarea.scrollTop = scrollPos;
}
// Update the saved userCode every time the user updates the text area code
textarea.onkeyup = function(){
// We only want to save the state when the user code is being shown,
// not the solution, so that solution is not saved over the user code
if(solution.value === 'Show solution') {
userEntry = textarea.value;
} else {
solutionEntry = textarea.value;
}
updateCode();
};
{{ EmbedLiveSample('Playable_code_2', '100%', 550, "", "", "hide-codepen-jsfiddle") }}
In this last exercise, the array contains a bunch of strings containing information about train stations in the North of England. The strings are data items that contain the three-letter station code, followed by some machine-readable data, followed by a semicolon, followed by the human-readable station name. For example:
MAN675847583748sjt567654;Manchester Piccadilly
We want to extract the station code and name, and put them together in a string with the following structure:
MAN: Manchester Piccadilly
We'd recommend doing it like this:
result variable to equal to the final string, not the input.<h2>Live output</h2>
<div class="output" style="min-height: 125px;">
<ul>
</ul>
</div>
<h2>Editable code</h2>
<p class="a11y-label">Press Esc to move focus away from the code area (Tab inserts a tab character).</p>
<textarea id="code" class="playable-code" style="height: 285px; width: 95%">
var list = document.querySelector('.output ul');
list.innerHTML = '';
var stations = ['MAN675847583748sjt567654;Manchester Piccadilly',
'GNF576746573fhdg4737dh4;Greenfield',
'LIV5hg65hd737456236dch46dg4;Liverpool Lime Street',
'SYB4f65hf75f736463;Stalybridge',
'HUD5767ghtyfyr4536dh45dg45dg3;Huddersfield'];
for (var i = 0; i < stations.length; i++) {
var input = stations[i];
// write your code just below here
var result = input;
var listItem = document.createElement('li');
listItem.textContent = result;
list.appendChild(listItem);
}
</textarea>
<div class="playable-buttons">
<input id="reset" type="button" value="Reset">
<input id="solution" type="button" value="Show solution">
</div>
html {
font-family: sans-serif;
}
h2 {
font-size: 16px;
}
.a11y-label {
margin: 0;
text-align: right;
font-size: 0.7rem;
width: 98%;
}
body {
margin: 10px;
background: #f5f9fa;
}
var textarea = document.getElementById('code');
var reset = document.getElementById('reset');
var solution = document.getElementById('solution');
var code = textarea.value;
var userEntry = textarea.value;
function updateCode() {
eval(textarea.value);
}
reset.addEventListener('click', function() {
textarea.value = code;
userEntry = textarea.value;
solutionEntry = jsSolution;
solution.value = 'Show solution';
updateCode();
});
solution.addEventListener('click', function() {
if(solution.value === 'Show solution') {
textarea.value = solutionEntry;
solution.value = 'Hide solution';
} else {
textarea.value = userEntry;
solution.value = 'Show solution';
}
updateCode();
});
var jsSolution = 'var list = document.querySelector(\'.output ul\');\nlist.innerHTML = \'\';\nvar stations = [\'MAN675847583748sjt567654;Manchester Piccadilly\',\n \'GNF576746573fhdg4737dh4;Greenfield\',\n \'LIV5hg65hd737456236dch46dg4;Liverpool Lime Street\',\n \'SYB4f65hf75f736463;Stalybridge\',\n \'HUD5767ghtyfyr4536dh45dg45dg3;Huddersfield\'];\n\nfor(var i = 0; i < stations.length; i++) {\n var input = stations[i];\n var code = input.slice(0,3);\n var semiC = input.indexOf(\';\');\n var name = input.slice(semiC + 1);\n var result = code + \': \' + name;\n var listItem = document.createElement(\'li\');\n listItem.textContent = result;\n list.appendChild(listItem);\n}';
var solutionEntry = jsSolution;
textarea.addEventListener('input', updateCode);
window.addEventListener('load', updateCode);
// stop tab key tabbing out of textarea and
// make it write a tab at the caret position instead
textarea.onkeydown = function(e){
if (e.keyCode === 9) {
e.preventDefault();
insertAtCaret('\t');
}
if (e.keyCode === 27) {
textarea.blur();
}
};
function insertAtCaret(text) {
var scrollPos = textarea.scrollTop;
var caretPos = textarea.selectionStart;
var front = (textarea.value).substring(0, caretPos);
var back = (textarea.value).substring(textarea.selectionEnd, textarea.value.length);
textarea.value = front + text + back;
caretPos = caretPos + text.length;
textarea.selectionStart = caretPos;
textarea.selectionEnd = caretPos;
textarea.focus();
textarea.scrollTop = scrollPos;
}
// Update the saved userCode every time the user updates the text area code
textarea.onkeyup = function(){
// We only want to save the state when the user code is being shown,
// not the solution, so that solution is not saved over the user code
if(solution.value === 'Show solution') {
userEntry = textarea.value;
} else {
solutionEntry = textarea.value;
}
updateCode();
};
{{ EmbedLiveSample('Playable_code_3', '100%', 585, "", "", "hide-codepen-jsfiddle") }}
不可否認當網站在跟人們互相溝通時，處理文字和句子在程式設計中是相當重要的，尤其是在 JavaScript 中。這篇文章已經傳授你如何去處理字串的方法，應該對以後深入了解其他更複雜主題的你會很有幫助。接下來，我們將會看看最後一個近期內我們需要關注的主要的資料型態 — 陣列。
{{PreviousMenuNext("Learn/JavaScript/First_steps/Strings", "Learn/JavaScript/First_steps/Arrays", "Learn/JavaScript/First_steps")}}