Boolean

Boolean object is an object wrapper for a boolean value.

描述

The value passed as the first parameter is converted to a boolean value, if necessary. If the value is omitted or is 0 , -0 , null , false , NaN , undefined , or the empty string ( "" ), the object has an initial value of false . All other values, including any object, an empty array ( [] ), or the string " false ", create an object with an initial value of true .

Do not confuse the primitive Boolean values true and false with the true and false values of the Boolean 对象。

Any object of which the value is not undefined or null , including a Boolean object whose value is false , evaluates to true when passed to a conditional statement. For example, the condition in the following if statement evaluates to true :

var x = new Boolean(false);
if (x) {
  // this code is executed
}
					

This behavior does not apply to Boolean primitives. For example, the condition in the following if statement evaluates to false :

var x = false;
if (x) {
  // this code is not executed
}
					

Do not use a Boolean object to convert a non-boolean value to a boolean value. To perform this task, instead, use Boolean as a function, or a double NOT operator :

var x = Boolean(expression);     // use this...
var x = !!(expression);          // ...or this
var x = new Boolean(expression); // don't use this!
					

If you specify any object, including a Boolean object whose value is false , as the initial value of a Boolean object, the new Boolean object has a value of true .

var myFalse = new Boolean(false);   // initial value of false
var g = Boolean(myFalse);       // initial value of true
var myString = new String('Hello'); // string object
var s = Boolean(myString);      // initial value of true
					

Do not use a Boolean object in place of a Boolean primitive.

注意: When the non-standard property document.all is used as an argument for this constructor, the result is a Boolean object with the value false . This property is legacy and non-standard and should not be used.

构造函数

Boolean()
创建新的 Boolean 对象。

实例方法

Boolean.prototype.toString()
Returns a string of either true or false depending upon the value of the object. Overrides the Object.prototype.toString() 方法。
Boolean.prototype.valueOf()
Returns the primitive value of the Boolean object. Overrides the Object.prototype.valueOf() 方法。

范例

Creating Boolean objects with an initial value of false

var bNoParam = new Boolean();
var bZero = new Boolean(0);
var bNull = new Boolean(null);
var bEmptyString = new Boolean('');
var bfalse = new Boolean(false);
					

创建 Boolean objects with an initial value of true

var btrue = new Boolean(true);
var btrueString = new Boolean('true');
var bfalseString = new Boolean('false');
var bSuLin = new Boolean('Su Lin');
var bArrayProto = new Boolean([]);
var bObjProto = new Boolean({});
					

规范

规范
ECMAScript (ECMA-262)
The definition of 'Boolean' in that specification.

浏览器兼容性

更新 GitHub 上的兼容性数据
Desktop Mobile Server
Chrome Edge Firefox Internet Explorer Opera Safari Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet Node.js
Boolean Chrome 1 Edge 12 Firefox 1 IE 3 Opera 3 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
Boolean() 构造函数 Chrome 1 Edge 12 Firefox 1 IE 3 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
toSource
非标
Chrome No Edge No Firefox 1 — 74
1 — 74
Starting in Firefox 74, toSource() is no longer available for use by web content. It is still allowed for internal and privileged code.
IE No Opera No Safari No WebView Android No Chrome Android No Firefox Android 4 Opera Android No Safari iOS No Samsung Internet Android No nodejs No
toString Chrome 1 Edge 12 Firefox 1 IE 3 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100
valueOf Chrome 1 Edge 12 Firefox 1 IE 4 Opera 4 Safari 1 WebView Android 1 Chrome Android 18 Firefox Android 4 Opera Android 10.1 Safari iOS 1 Samsung Internet Android 1.0 nodejs 0.1.100

图例

完整支持
完整支持
不支持
不支持
非标。预期跨浏览器支持较差。
见实现注意事项。

另请参阅

Metadata