From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../reference/global_objects/json/parse/index.html | 224 +++++++++++++++++++++ 1 file changed, 224 insertions(+) create mode 100644 files/zh-cn/web/javascript/reference/global_objects/json/parse/index.html (limited to 'files/zh-cn/web/javascript/reference/global_objects/json/parse') diff --git a/files/zh-cn/web/javascript/reference/global_objects/json/parse/index.html b/files/zh-cn/web/javascript/reference/global_objects/json/parse/index.html new file mode 100644 index 0000000000..e1e970a1e4 --- /dev/null +++ b/files/zh-cn/web/javascript/reference/global_objects/json/parse/index.html @@ -0,0 +1,224 @@ +--- +title: JSON.parse() +slug: Web/JavaScript/Reference/Global_Objects/JSON/parse +tags: + - ECMAScript 5 + - JSON + - JavaScript + - 参考 + - 方法 +translation_of: Web/JavaScript/Reference/Global_Objects/JSON/parse +--- +
{{JSRef}}
+ +

JSON.parse() 方法用来解析JSON字符串，构造由字符串描述的JavaScript值或对象。提供可选的 reviver 函数用以在返回之前对所得到的对象执行变换(操作)。

+ +
{{EmbedInteractiveExample("pages/js/json-parse.html")}}
+ + + +

语法

+ +
JSON.parse(text[, reviver])
+ +

参数

+ +
+
text
+
要被解析成 JavaScript 值的字符串，关于JSON的语法格式,请参考：{{jsxref("JSON")}}。
+
reviver {{optional_inline()}}
+
转换器, 如果传入该参数(函数)，可以用来修改解析生成的原始值，调用时机在 parse 函数返回之前。
+
+ +

返回值

+ +

{{jsxref("Object")}} 类型, 对应给定 JSON 文本的对象/值。

+ +

异常

+ +

若传入的字符串不符合 JSON 规范，则会抛出 {{jsxref("SyntaxError")}} 异常。

+ +

示例

+ +

使用 JSON.parse()

+ +
JSON.parse('{}');              // {}
+JSON.parse('true');            // true
+JSON.parse('"foo"');           // "foo"
+JSON.parse('[1, 5, "false"]'); // [1, 5, "false"]
+JSON.parse('null');            // null
+
+ +

使用 reviver 函数

+ +

如果指定了 reviver 函数，则解析出的 JavaScript 值（解析值）会经过一次转换后才将被最终返回（返回值）。更具体点讲就是：解析值本身以及它所包含的所有属性，会按照一定的顺序（从最最里层的属性开始，一级级往外，最终到达顶层，也就是解析值本身）分别的去调用 reviver 函数，在调用过程中，当前属性所属的对象会作为 this 值，当前属性名和属性值会分别作为第一个和第二个参数传入 reviver 中。如果 reviver 返回 undefined，则当前属性会从所属对象中删除，如果返回了其他值，则返回的值会成为当前属性新的属性值。

+ +

当遍历到最顶层的值（解析值）时，传入 reviver 函数的参数会是空字符串 ""（因为此时已经没有真正的属性）和当前的解析值（有可能已经被修改过了），当前的 this 值会是 {"": 修改过的解析值}，在编写 reviver 函数时，要注意到这个特例。（这个函数的遍历顺序依照：从最内层开始，按照层级顺序，依次向外遍历）

+ +
JSON.parse('{"p": 5}', function (k, v) {
+    if(k === '') return v;     // 如果到了最顶层，则直接返回属性值，
+    return v * 2;              // 否则将属性值变为原来的 2 倍。
+});                            // { p: 10 }
+
+JSON.parse('{"1": 1, "2": 2,"3": {"4": 4, "5": {"6": 6}}}', function (k, v) {
+    console.log(k); // 输出当前的属性名，从而得知遍历顺序是从内向外的，
+                    // 最后一个属性名会是个空字符串。
+    return v;       // 返回原始属性值，相当于没有传递 reviver 参数。
+});
+
+// 1
+// 2
+// 4
+// 6
+// 5
+// 3
+// ""
+
+ +

JSON.parse() 不允许用逗号作为结尾

+ +
// both will throw a SyntaxError
+JSON.parse("[1, 2, 3, 4, ]");
+JSON.parse('{"foo" : 1, }');
+
+ +

Polyfill

+ +
// From https://github.com/douglascrockford/JSON-js/blob/master/json2.js
+if (typeof JSON.parse !== "function") {
+    var rx_one = /^[\],:{}\s]*$/;
+    var rx_two = /\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g;
+    var rx_three = /"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g;
+    var rx_four = /(?:^|:|,)(?:\s*\[)+/g;
+    var rx_dangerous = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g;
+    JSON.parse = function(text, reviver) {
+
+        // The parse method takes a text and an optional reviver function, and returns
+        // a JavaScript value if the text is a valid JSON text.
+
+        var j;
+
+        function walk(holder, key) {
+
+            // The walk method is used to recursively walk the resulting structure so
+            // that modifications can be made.
+
+            var k;
+            var v;
+            var value = holder[key];
+            if (value && typeof value === "object") {
+                for (k in value) {
+                    if (Object.prototype.hasOwnProperty.call(value, k)) {
+                        v = walk(value, k);
+                        if (v !== undefined) {
+                            value[k] = v;
+                        } else {
+                            delete value[k];
+                        }
+                    }
+                }
+            }
+            return reviver.call(holder, key, value);
+        }
+
+
+        // Parsing happens in four stages. In the first stage, we replace certain
+        // Unicode characters with escape sequences. JavaScript handles many characters
+        // incorrectly, either silently deleting them, or treating them as line endings.
+
+        text = String(text);
+        rx_dangerous.lastIndex = 0;
+        if (rx_dangerous.test(text)) {
+            text = text.replace(rx_dangerous, function(a) {
+                return (
+                    "\\u" +
+                    ("0000" + a.charCodeAt(0).toString(16)).slice(-4)
+                );
+            });
+        }
+
+        // In the second stage, we run the text against regular expressions that look
+        // for non-JSON patterns. We are especially concerned with "()" and "new"
+        // because they can cause invocation, and "=" because it can cause mutation.
+        // But just to be safe, we want to reject all unexpected forms.
+
+        // We split the second stage into 4 regexp operations in order to work around
+        // crippling inefficiencies in IE's and Safari's regexp engines. First we
+        // replace the JSON backslash pairs with "@" (a non-JSON character). Second, we
+        // replace all simple value tokens with "]" characters. Third, we delete all
+        // open brackets that follow a colon or comma or that begin the text. Finally,
+        // we look to see that the remaining characters are only whitespace or "]" or
+        // "," or ":" or "{" or "}". If that is so, then the text is safe for eval.
+
+        if (
+            rx_one.test(
+                text
+                .replace(rx_two, "@")
+                .replace(rx_three, "]")
+                .replace(rx_four, "")
+            )
+        ) {
+
+            // In the third stage we use the eval function to compile the text into a
+            // JavaScript structure. The "{" operator is subject to a syntactic ambiguity
+            // in JavaScript: it can begin a block or an object literal. We wrap the text
+            // in parens to eliminate the ambiguity.
+
+            j = eval("(" + text + ")");
+
+            // In the optional fourth stage, we recursively walk the new structure, passing
+            // each name/value pair to a reviver function for possible transformation.
+
+            return (typeof reviver === "function") ?
+                walk({
+                    "": j
+                }, "") :
+                j;
+        }
+
+        // If the text is not JSON parseable, then a SyntaxError is thrown.
+
+        throw new SyntaxError("JSON.parse");
+    };
+}
+ +

规范

+ + + + + + + + + + + + + + + + + + + + + + + + +
规范名称规范状态备注
{{SpecName('ES5.1', '#sec-15.12.2', 'JSON.parse')}}{{Spec2('ES5.1')}}首次定义，于 JavaScript 1.7 版本中实现。
{{SpecName('ES6', '#sec-json.parse', 'JSON.parse')}}{{Spec2('ES6')}}
{{SpecName('ESDraft', '#sec-json.parse', 'JSON.parse')}}{{Spec2('ESDraft')}}
+ +

浏览器兼容性

+ +
+ + +

{{Compat("javascript.builtins.JSON.parse")}}

+
+ +

相关链接

+ + -- cgit v1.2.3-54-g00ecf