javascript 字符串转换为 undefined/null/number/boolean
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原文地址: http://stackoverflow.com/questions/18799685/
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String conversion to undefined/null/number/boolean
提问by Gabriel Llamas
Do you know any better and faster way to convert a string to the type it represents?
您知道将字符串转换为它所代表的类型的更好更快的方法吗？
I've always been using this function:
我一直在使用这个功能：
var convertType = function (value){
if (value === "undefined") return undefined;
if (value === "null") return null;
if (value === "true") return true;
if (value === "false") return false;
var v = Number (value);
return isNaN (v) ? value : v;
};
Candidates:
考生：
//Me, Gabriel Llamas
var cast1 = function (value){
if (value === "undefined") return undefined;
if (value === "null") return null;
if (value === "true") return true;
if (value === "false") return false;
var v = Number (value);
return isNaN (v) ? value : v;
};
//KooiInc
var cast2 = function (value){
var v = Number (value);
return !isNaN(v) ? v :
value === "undefined" ? undefined
: value === "null" ? null
: value === "true" ? true
: value === "false" ? false
: value
};
//LightStyle
var cast3 = function (value){
try {
return (new Function("return " + value + ";"))();
} catch(e) {
return value;
}
};
//Emmissary's proposal
var cast4 = function (value){
if (value === "undefined") return undefined;
try{
return JSON.parse (value);
}catch (e){
return value;
}
};
Benchmark code (using speedy):
基准代码（使用speedy）：
var fn = function (cast){
cast ("undefined");
cast ("null");
cast ("true");
cast ("false");
cast ("12");
cast ("12.34");
cast ("asd");
};
speedy.run ({
"cast 1": function (){
fn (cast1);
},
"cast 2": function (){
fn (cast2);
},
"cast 3": function (){
fn (cast3);
},
"cast 4": function (){
fn (cast4);
}
});
Result:
结果：
File: string-conversion.js
Node v0.10.18
V8 v3.14.5.9
Speedy v0.0.8
Benchmarks: 4
Timeout: 1000ms (1s 0ms)
Samples: 3
Total time per benchmark: ~3000ms (3s 0ms)
Total time: ~12000ms (12s 0ms)
Higher is better (ops/sec)
cast 1
6,270,458 ± 0.2%
cast 2
3,305,103 ± 0.0%
cast 3
54,952 ± 0.0%
cast 4
82,790 ± 0.4%
Elapsed time: 12109ms (12s 109ms)
回答by Niccolò Campolungo
This is a simple function which involves the use of a function to evaluate the strings. This way you can remove the part of cases' "switch". Be aware that this handles also assignments to global variables, so I recommend it only if you know anytime where is the source from(don't allow users to use this function!)
这是一个简单的函数，它涉及使用函数来评估字符串。这样您就可以删除案例的“开关”部分。请注意，这也处理对全局变量的分配，因此只有当您随时知道源来自何处时，我才推荐它（不允许用户使用此函数！）
var convertType = function (value){
try {
return (new Function("return " + value + ";"))();
} catch(e) {
return value;
}
};
You can see the jsfiddle here.
回答by KooiInc
How about:
怎么样：
var convertType = function (value){
var values = {undefined: undefined, null: null, true: true, false: false}
,isNumber = !isNaN(+(value));
return isNumber && +(value) || !(value in values) && value || values[value];
};
convertType('null'); //=> null
convertType('something'); //=> "something"
convertType('57.321'); //=> 57.321
convertType('undefined'); //=> undefined
This seems faster @ jsPerf
这似乎更快@ jsPerf
var convertType = function (value){
var v = Number (value);
return !isNaN(v) ? v :
value === "undefined" ? undefined
: value === "null" ? null
: value === "true" ? true
: value === "false" ? false
: value
}
回答by suffering
var string2literal = function (value){
var maps = {
"NaN": NaN,
"null": null,
"undefined": undefined,
"Infinity": Infinity,
"-Infinity": -Infinity
}
return ((value in maps) ? maps[value] : value);
};
There are many weird rules in dynamic data type converting, just map it.
动态数据类型转换有很多奇怪的规则，映射一下就行了。
