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)。
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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:
JSON
。 -
reviver
可选 - 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
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 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 |
---|---|---|
ECMAScript 5.1 (ECMA-262) JSON.parse |
Standard | 首次定义,于 JavaScript 1.7 版本中实现。 |
ECMAScript 2015 (6th Edition, ECMA-262) JSON.parse |
Standard | |
ECMAScript Latest Draft (ECMA-262) JSON.parse |
Draft |
浏览器兼容性
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
parse |
Chrome Full support 3 | Edge Full support 12 | Firefox Full support 3.5 | IE Full support 8 | Opera Full support 10.5 | Safari Full support 4 | WebView Android Full support ≤37 | Chrome Android Full support 18 | Firefox Android Full support 4 | Opera Android Full support 11 | Safari iOS Full support Yes | Samsung Internet Android Full support 1.0 | nodejs Full support Yes |
Legend
- Full support
- Full support