来源
《JavaScript语言精粹（修订版）》
代码
<!DOCTYPE html>
<html> <head>
<meta charset="UTF-8">
<title></title>
</head> <body>
<script>
var json_parse = function () {
var
at,
ch,
escapee = {
'"': '"',
'\\': '\\',
'/': '/',
b: 'b',
f: '\f',
n: '\n',
r: '\r',
t: '\t'
},
text,
// 抛出异常
error = function (m) {
throw {
name: 'SyntaxError',
message: m,
at: at,
text: text
}
},
// 获取下一个字符
next = function (c) {
if (c && c !== ch) {
error(`Expected ${c} instead of ${ch}`);
}
ch = text.charAt(at);
at += 1;
return ch;
},
// 解析一个数字值
number = function () {
var number, string = '';
// 负号
if (ch === '-') {
string = '-',
next('-')
}
// 整数
while (ch >= '0' && ch <= '9') {
string += ch;
next();
}
// 小数
if (ch === '.') {
string += '.';
while (next() && ch >= '0' && ch <= '9') {
string += ch;
}
}
// 指数
if (ch === 'e' || ch === 'E') {
string += ch;
next();
if (ch === '-' || ch === '+') {
string += ch;
next();
}
while (ch >= '0' && ch <= '9') {
string += ch;
next();
}
}
number = +string;
if (isNaN(number)) {
error('Bad number')
} else {
return number;
}
},
// 解析一个字符串值
string = function () {
var hex,
i,
string = '',
uffff;
// 字符串必须以双引号开始
if (ch === '"') {
while (next()) {
if (ch === '"') {
next();
return string;
} else if (ch === '\\') {
next();
// unicode码
if (ch === 'u') {
uffff = 0;
for (i = 0; i < 4; i++) {
hex = parseInt(next(), 16);
if (!isFinite(hex)) {
break;
}
ufff = ufff * 16 + hex;
}
string += String.fromCharCode(ufff)
}
else if (typeof escapee[ch] === 'string') { // 转义字符
string += escapee[ch]
} else {
break;
}
} else {
string += ch;
}
}
}
error('Bac string');
},
// 跳过空白
white = function () {
while (ch && ch <= ' ') {
next();
}
},
// 解析 true、false、null
word = function () {
switch (ch) {
case 't':
next('t');
next('r');
next('u');
next('e');
return true;
case 'f':
next('f');
next('a');
next('l');
next('s');
next('e');
return true;
case 'n':
next('n');
next('u');
next('l');
next('l');
return true;
}
error(`Unexpected ${ch}`)
},
// 解析一个数组值
array = function () {
var array = [];
if (ch === '[') {
next('[');
white();
if (ch === ']') {
next(']');
return array;
}
while (ch) {
array.push(value());
white();
if (ch === ']') {
next(']');
return array;
}
next(',');
white();
}
}
error('Bad array');
},
// 解析一个对象值
object = function () {
var key, object = {};
if (ch === '{') {
next('{');
white();
if (ch === '}') {
next('}');
return object;
}
while (ch) {
key = string();
white();
next(':');
object[key] = value();
white();
if (ch === '}') {
next('}');
return object;
}
next(',');
white();
}
}
error('Bad object');
},
// 解析一个JSON值。它可以是对象、数组、字符串、数字、一个词。
value = function () {
white();
switch (ch) {
case '{':
return object();
case '[':
return array();
case '"':
return string();
case '-':
return number;
default:
return ch >= '0' && ch <= '9' ? number() : word();
}
};
// 返回json_parse函数
return function (source, reviver) {
var result;
text = source;
at = 0;
ch = ' ';
result = value();
white();
if (ch) { // 多余的非空白字符
error('Syntax error');
}
return typeof reviver === 'function' ? function walk(holder, key) {
var k, v, value = holder[key];
if (value && typeof value === 'object') {
// 递归处理对象的属性
for (k in value) {
if (Object.hasOwnProperty.call(value, k)) {
v = walk(value, k);
if (v !== undefined) {
value[k] = v;
} else {
delete value[k]
}
}
}
}
// 处理对象
return reviver.call(holder, key, value);
}({ '': result }, '') : result;
}
}();
// \n是一个字符，\\n是两个字符
const str = '{"name":"饮料","price":2.5,"cool":true,"description":["雪碧","可乐"],"escapseSlash":"\\/","escapeN":"\\n"}';
console.log(json_parse(str, (key, val) => val))
</script>
</body> </html>
运行结果
