JSON.js 源码学习..
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<script type="text/javascript">
var JSON;
if (!JSON) {
JSON = {};
} (function () {
'use strict'; function f(n) {
// Format integers to have at least two digits.
// 补齐 两位数
return n < 10 ? '0' + n : n;
}
// 在高级浏览器调用
(new Date() ).toJSON()
"2017-07-28T01:27:34.790Z" , 所以下面是按照这个格式来模拟 if (typeof Date.prototype.toJSON !== 'function') { Date.prototype.toJSON = function (key) { return isFinite(this.valueOf())
? this.getUTCFullYear() + '-' +
f(this.getUTCMonth() + 1) + '-' +
f(this.getUTCDate()) + 'T' +
f(this.getUTCHours()) + ':' +
f(this.getUTCMinutes()) + ':' +
f(this.getUTCSeconds()) + 'Z'
: null;
};
//不支持toJSON 的浏览器可以取这些元素对象的 值
String.prototype.toJSON =
Number.prototype.toJSON =
Boolean.prototype.toJSON = function (key) {
return this.valueOf();
};
}
//过滤掉unicode特殊字符，
可以通过String.fromCharCode(parseInt(unicode),16)来输出，不过大部分unicode是『不可见』的，还是要通过unicode码表来查看
text.replace(/\\u[\dA-F]{4}/gi, function (match) { return String.fromCharCode(parseInt(match.replace(/\\u/g, ''), 16)); }); var cx = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
//一些讨厌的特殊字符
escapable = /[\\\"\x00-\x1f\x7f-\x9f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g,
gap,
indent,
meta = { // table of character substitutions 字符替换表格, 一些需要转义
'\b': '\\b',
'\t': '\\t',
'\n': '\\n',
'\f': '\\f',
'\r': '\\r',
'"' : '\\"',
'\\': '\\\\'
},
rep; function quote(string) { // If the string contains no control characters, no quote characters, and no
// backslash characters, then we can safely slap some quotes around it.
// Otherwise we must also replace the offending characters with safe escape
// sequences.
// 如果字符串包涵了 控制字符? 引号, 反斜杠, 我们就必须把这些讨厌的字符给替换成安全的, 否则我们把这些用引号给包裹起来,
escapable.lastIndex = 0;
return escapable.test(string) ? '"' + string.replace(escapable, function (a) {
var c = meta[a];
return typeof c === 'string'
? c
: '\\u' + ('0000' + a.charCodeAt(0).toString(16)).slice(-4);
}) + '"' : '"' + string + '"';
} function str(key, holder) { // Produce a string from holder[key]. var i, // The loop counter.
k, // The member key.
v, // The member value.
length,
mind = gap,
partial,
value = holder[key]; // If the value has a toJSON method, call it to obtain a replacement value.
// 如果有toJSON方法， 调用生成序列化字符串 if (value && typeof value === 'object' &&
typeof value.toJSON === 'function') {
value = value.toJSON(key);
} // If we were called with a replacer function, then call the replacer to
// obtain a replacement value. 如有有替代的函数 if (typeof rep === 'function') {
value = rep.call(holder, key, value);
} // What happens next depends on the value's type. vule的类型决定下一步干什么 switch (typeof value) {
case 'string':
return quote(value); case 'number': // JSON numbers must be finite. Encode non-finite numbers as null. 如果无限的值被转成 null return isFinite(value) ? String(value) : 'null'; case 'boolean':
case 'null': // If the value is a boolean or null, convert it to a string. Note:
// typeof null does not produce 'null'. The case is included here in
// the remote chance that this gets fixed someday.
// 如果值是 boolean null, 转成 'true' 'false' 'null'; 虽然typeof null 不会是‘null’ , 但以后有机会被修正成'null', 所以这里我们也把这种情况包含进来 return String(value); // If the type is 'object', we might be dealing with an object or an array or
// null. case 'object': // Due to a specification blunder in ECMAScript, typeof null is 'object',
// so watch out for that case. if (!value) {
return 'null';
} // Make an array to hold the partial results of stringifying this object value.
// 用一个数组保存部分已被序列化的结果
gap += indent;
partial = []; // Is the value an array? if (Object.prototype.toString.apply(value) === '[object Array]') { // The value is an array. Stringify every element. Use null as a placeholder
// for non-JSON values. length = value.length;
for (i = 0; i < length; i += 1) {
//如果数组， 递归调用str
partial[i] = str(i, value) || 'null';
} // Join all of the elements together, separated with commas, and wrap them in
// brackets. 组合所有的元素以前， 用逗号分隔， 用括号包裹 v = partial.length === 0
? '[]'
: gap
? '[\n' + gap + partial.join(',\n' + gap) + '\n' + mind + ']'
: '[' + partial.join(',') + ']';
gap = mind;
return v;
} // If the replacer is an array, use it to select the members to be stringified. if (rep && typeof rep === 'object') {
length = rep.length;
for (i = 0; i < length; i += 1) {
if (typeof rep[i] === 'string') {
k = rep[i];
v = str(k, value);
if (v) {
partial.push(quote(k) + (gap ? ': ' : ':') + v);
}
}
}
} else { // Otherwise, iterate through all of the keys in the object. for (k in value) {
if (Object.prototype.hasOwnProperty.call(value, k)) {
v = str(k, value);
if (v) {
partial.push(quote(k) + (gap ? ': ' : ':') + v);
}
}
}
} // Join all of the member texts together, separated with commas,
// and wrap them in braces. v = partial.length === 0
? '{}'
: gap
? '{\n' + gap + partial.join(',\n' + gap) + '\n' + mind + '}'
: '{' + partial.join(',') + '}';
gap = mind;
return v;
}
} // If the JSON object does not yet have a stringify method, give it one. if (typeof JSON.stringify !== 'function'||(navigator.userAgent.indexOf("MSIE 8.0")>0)) {
JSON.stringify = function (value, replacer, space) { // The stringify method takes a value and an optional replacer, and an optional
// space parameter, and returns a JSON text. The replacer can be a function
// that can replace values, or an array of strings that will select the keys.
// A default replacer method can be provided. Use of the space parameter can
// produce text that is more easily readable. var i;
gap = '';
indent = ''; // If the space parameter is a number, make an indent string containing that
// many spaces. if (typeof space === 'number') {
for (i = 0; i < space; i += 1) {
indent += ' ';
} // If the space parameter is a string, it will be used as the indent string. } else if (typeof space === 'string') {
indent = space;
} // If there is a replacer, it must be a function or an array.
// Otherwise, throw an error. rep = replacer;
if (replacer && typeof replacer !== 'function' &&
(typeof replacer !== 'object' ||
typeof replacer.length !== 'number')) {
throw new Error('JSON.stringify');
} // Make a fake root object containing our value under the key of ''.
// Return the result of stringifying the value. return str('', {'': value});
};
} // If the JSON object does not yet have a parse method, give it one. if (typeof JSON.parse !== 'function') {
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, v, 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);
cx.lastIndex = 0;
if (cx.test(text)) {
text = text.replace(cx, 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. //先把无意义的 字符替换成空, 在看看结果是不是符合JSON格式
if (/^[\],:{}\s]*$/
.test(text.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '@')
.replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']')
.replace(/(?:^|:|,)(?:\s*\[)+/g, ''))) { // 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');
};
}
}()); </script> </body>
</html>
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