140-----JS基础-----JSON
作者：互联网
一 代码
到本节，js的基础算学完了，由于个人是C++方向的，所以学习js只是为了学习基础的语法，因为有时候看源码需要用到，不得不去学一下，但不会往太深的方向发展。
个人觉得如果是后台开发只需要深入学习一到两门主语即可。
1 IE7以上以及其它各种浏览器使用JSON的方法
JSON的操作很简单，就需要了解下面两个函数JSON.parse、JSON.stringify即可。
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<!--
1. 如果需要兼容IE7及以下的JSON操作，则可以通过引入一个外部的js文件来处理。
我们用的时候直接拷贝json2.js的内容即可，是自己写的一个JSON对象。
-->
<script type="text/javascript" src="js/json2.js"></script>
<script type="text/javascript">
/*
* 2. JSON
* - JS中的对象只有JS自己认识，其他的语言都不认识
* - JSON就是一个特殊格式的字符串，这个字符串可以被任意的语言所识别，
* 并且可以转换为任意语言中的对象，JSON在开发中主要用来数据的交互
* - JSON
* - JavaScript Object Notation JS对象表示法
* - JSON和JS对象的格式一样，只不过JSON字符串中的属性名必须加双引号
* 其他的和JS语法一致
* JSON分类：
* 1.对象 {}
* 2.数组 []
*
* JSON中允许的值：
* 1.字符串
* 2.数值
* 3.布尔值
* 4.null
* 5.对象
* 6.数组
*/
//创建一个对象
var arr = '[1,2,3,"hello",true]';
var obj2 = '{"arr":[1,2,3]}';
var arr2 ='[{"name":"孙悟空","age":18,"gender":"男"},{"name":"孙悟空","age":18,"gender":"男"}]';
/*
* 3. 将JSON字符串转换为JS中的对象
* 在JS中，为我们提供了一个工具类，就叫JSON
* 这个对象可以帮助我们将一个JSON转换为JS对象，也可以将一个JS对象转换为JSON
*/
var json = '{"name":"孙悟空","age":18,"gender":"男"}';
/*
* 4. json --> js对象
* JSON.parse()
* - 可以将以JSON字符串转换为js对象
* - 它需要一个JSON字符串作为参数，会将该字符串转换为JS对象并返回
*/
var o = JSON.parse(json);
var o2 = JSON.parse(arr);
//console.log(o.gender);
//console.log(o2[1]);
var obj3 = {name:"猪八戒" , age:28 , gender:"男"};
/*
* 5. JS对象 ---> JSON
* JSON.stringify()
* - 可以将一个JS对象转换为JSON字符串
* - 需要一个js对象作为参数，会返回一个JSON字符串
*/
var str = JSON.stringify(obj3);
//console.log(str);
/*
**加粗样式** * 6. JSON这个对象在IE7及以下的浏览器中不支持，所以在这些浏览器中调用时会报错
*/
var str3 = '{"name":"孙悟空","age":18,"gender":"男"}';
JSON.parse(str3);
</script>
</head>
<body>
</body>
</html>
但是由于IE7以下不支持上面的JSON对象，所以需要自己去处理。例如有下面两种方法，不建议使用eval()，因为它的执行性能比较差，然后它还具有安全隐患。
建议使用自己写的代码。
2 IE7支持JSON的方法：
2.1 方法1(不建议)：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<script type="text/javascript">
var str = '{"name":"孙悟空","age":18,"gender":"男"}';
/*
* 1. eval()
* - 这个函数可以用来执行一段字符串形式的JS代码，并将执行结果返回
* - 如果使用eval()执行的字符串中含有{},它会将{}当成是代码块
* 如果不希望将其当成代码块解析，则需要在字符串前后各加一个()
*
* - eval()这个函数的功能很强大，可以直接执行一个字符串中的js代码，
* 但是在开发中尽量不要使用，首先它的执行性能比较差，然后它还具有安全隐患
*/
var str2 = "alert('hello');";
var obj = eval("("+str+")");
//console.log(obj);
</script>
</head>
<body>
</body>
</html>
2.2 方法2(建议)：
// json2.js
// 2016-05-01
// Public Domain.
// NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
// See http://www.JSON.org/js.html
// This code should be minified before deployment.
// See http://javascript.crockford.com/jsmin.html
// USE YOUR OWN COPY. IT IS EXTREMELY UNWISE TO LOAD CODE FROM SERVERS YOU DO
// NOT CONTROL.
// This file creates a global JSON object containing two methods: stringify
// and parse. This file is provides the ES5 JSON capability to ES3 systems.
// If a project might run on IE8 or earlier, then this file should be included.
// This file does nothing on ES5 systems.
// JSON.stringify(value, replacer, space)
// value any JavaScript value, usually an object or array.
// replacer an optional parameter that determines how object
// values are stringified for objects. It can be a
// function or an array of strings.
// space an optional parameter that specifies the indentation
// of nested structures. If it is omitted, the text will
// be packed without extra whitespace. If it is a number,
// it will specify the number of spaces to indent at each
// level. If it is a string (such as "\t" or " "),
// it contains the characters used to indent at each level.
// This method produces a JSON text from a JavaScript value.
// When an object value is found, if the object contains a toJSON
// method, its toJSON method will be called and the result will be
// stringified. A toJSON method does not serialize: it returns the
// value represented by the name/value pair that should be serialized,
// or undefined if nothing should be serialized. The toJSON method
// will be passed the key associated with the value, and this will be
// bound to the value.
// For example, this would serialize Dates as ISO strings.
// Date.prototype.toJSON = function (key) {
// function f(n) {
// // Format integers to have at least two digits.
// return (n < 10)
// ? "0" + n
// : n;
// }
// return this.getUTCFullYear() + "-" +
// f(this.getUTCMonth() + 1) + "-" +
// f(this.getUTCDate()) + "T" +
// f(this.getUTCHours()) + ":" +
// f(this.getUTCMinutes()) + ":" +
// f(this.getUTCSeconds()) + "Z";
// };
// You can provide an optional replacer method. It will be passed the
// key and value of each member, with this bound to the containing
// object. The value that is returned from your method will be
// serialized. If your method returns undefined, then the member will
// be excluded from the serialization.
// If the replacer parameter is an array of strings, then it will be
// used to select the members to be serialized. It filters the results
// such that only members with keys listed in the replacer array are
// stringified.
// Values that do not have JSON representations, such as undefined or
// functions, will not be serialized. Such values in objects will be
// dropped; in arrays they will be replaced with null. You can use
// a replacer function to replace those with JSON values.
// JSON.stringify(undefined) returns undefined.
// The optional space parameter produces a stringification of the
// value that is filled with line breaks and indentation to make it
// easier to read.
// If the space parameter is a non-empty string, then that string will
// be used for indentation. If the space parameter is a number, then
// the indentation will be that many spaces.
// Example:
// text = JSON.stringify(["e", {pluribus: "unum"}]);
// // text is '["e",{"pluribus":"unum"}]'
// text = JSON.stringify(["e", {pluribus: "unum"}], null, "\t");
// // text is '[\n\t"e",\n\t{\n\t\t"pluribus": "unum"\n\t}\n]'
// text = JSON.stringify([new Date()], function (key, value) {
// return this[key] instanceof Date
// ? "Date(" + this[key] + ")"
// : value;
// });
// // text is '["Date(---current time---)"]'
// JSON.parse(text, reviver)
// This method parses a JSON text to produce an object or array.
// It can throw a SyntaxError exception.
// The optional reviver parameter is a function that can filter and
// transform the results. It receives each of the keys and values,
// and its return value is used instead of the original value.
// If it returns what it received, then the structure is not modified.
// If it returns undefined then the member is deleted.
// Example:
// // Parse the text. Values that look like ISO date strings will
// // be converted to Date objects.
// myData = JSON.parse(text, function (key, value) {
// var a;
// if (typeof value === "string") {
// a =
// /^(\d{4})-(\d{2})-(\d{2})T(\d{2}):(\d{2}):(\d{2}(?:\.\d*)?)Z$/.exec(value);
// if (a) {
// return new Date(Date.UTC(+a[1], +a[2] - 1, +a[3], +a[4],
// +a[5], +a[6]));
// }
// }
// return value;
// });
// myData = JSON.parse('["Date(09/09/2001)"]', function (key, value) {
// var d;
// if (typeof value === "string" &&
// value.slice(0, 5) === "Date(" &&
// value.slice(-1) === ")") {
// d = new Date(value.slice(5, -1));
// if (d) {
// return d;
// }
// }
// return value;
// });
// This is a reference implementation. You are free to copy, modify, or
// redistribute.
/*jslint
eval, for, this
*/
/*property
JSON, apply, call, charCodeAt, getUTCDate, getUTCFullYear, getUTCHours,
getUTCMinutes, getUTCMonth, getUTCSeconds, hasOwnProperty, join,
lastIndex, length, parse, prototype, push, replace, slice, stringify,
test, toJSON, toString, valueOf
*/
// Create a JSON object only if one does not already exist. We create the
// methods in a closure to avoid creating global variables.
if (typeof JSON !== "object") {
JSON = {};
}
(function () {
"use strict";
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_escapable = /[\\\"\u0000-\u001f\u007f-\u009f\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g;
var rx_dangerous = /[\u0000\u00ad\u0600-\u0604\u070f\u17b4\u17b5\u200c-\u200f\u2028-\u202f\u2060-\u206f\ufeff\ufff0-\uffff]/g;
function f(n) {
// Format integers to have at least two digits.
return n < 10
? "0" + n
: n;
}
function this_value() {
return this.valueOf();
}
if (typeof Date.prototype.toJSON !== "function") {
Date.prototype.toJSON = function () {
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;
};
Boolean.prototype.toJSON = this_value;
Number.prototype.toJSON = this_value;
String.prototype.toJSON = this_value;
}
var gap;
var indent;
var meta;
var 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.
rx_escapable.lastIndex = 0;
return rx_escapable.test(string)
? "\"" + string.replace(rx_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.
var k; // The member key.
var v; // The member value.
var length;
var mind = gap;
var partial;
var value = holder[key];
// If the value has a toJSON method, call it to obtain a replacement value.
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.
if (typeof rep === "function") {
value = rep.call(holder, key, value);
}
// What happens next depends on the value's type.
switch (typeof value) {
case "string":
return quote(value);
case "number":
// JSON numbers must be finite. Encode non-finite numbers as 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.
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.
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) {
partial[i] = str(i, value) || "null";
}
// Join all of the elements together, separated with commas, and wrap them in
// brackets.
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") {
meta = { // table of character substitutions
"\b": "\\b",
"\t": "\\t",
"\n": "\\n",
"\f": "\\f",
"\r": "\\r",
"\"": "\\\"",
"\\": "\\\\"
};
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;
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");
};
}
}());
标签：function,140,text,object,value,JSON,-----,var 来源： https://blog.csdn.net/weixin_44517656/article/details/121567881