Object.prototype.toString()

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句法
描述
参数
范例
规范
浏览器兼容性
另请参阅
相关话题

toString() method returns a string representing the object.

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句法

obj.toString()

返回值

A string representing the object.

描述

Every object has a toString() method that is automatically called when the object is to be represented as a text value or when an object is referred to in a manner in which a string is expected. By default, the toString() method is inherited by every object descended from Object . If this method is not overridden in a custom object, toString() returns " [object type ] ", where type is the object type. The following code illustrates this:

const o = new Object();
o.toString(); // returns [object Object]

注意： Starting in JavaScript 1.8.5, toString() called on null 返回 [object Null ] ，和 undefined 返回 [object Undefined ] , as defined in the 5 ^th Edition of ECMAScript and subsequent Errata.

见使用 toString() to detect object class .

参数

For Numbers and BigInts toString() takes an optional parameter radix the value of radix must be minimum 2 and maximum 36.

By using radix you can also convert base 10 numbers (like 1,2,3,4,5,.........) to another base numbers, in example below we are converting base 10 number to a base 2 (binary) number

let baseTenInt = 10;
console.log(baseTenInt.toString(2));
// Expected output is "1010"

and same for big integers

let bigNum = BigInt(20);
console.log(bigNum.toString(2));
// Expected output is "10100"

Some common radix are

范例

Overriding the default `toString` 方法

You can create a function to be called in place of the default toString() method. The toString() method takes no arguments and should return a string. The toString() method you create can be any value you want, but it will be most useful if it carries information about the object.

The following code defines the Dog object type and creates theDog , an object of type Dog :

function Dog(name, breed, color, sex) {
  this.name = name;
  this.breed = breed;
  this.color = color;
  this.sex = sex;
}
theDog = new Dog('Gabby', 'Lab', 'chocolate', 'female');

If you call the toString() method on this custom object, it returns the default value inherited from Object :

theDog.toString(); // returns [object Object]

The following code creates and assigns dogToString() to override the default toString() method. This function generates a string containing the name , breed , color ，和 sex of the object, in the form " property = value; ".

Dog.prototype.toString = function dogToString() {
  const ret = 'Dog ' + this.name + ' is a ' + this.sex + ' ' + this.color + ' ' + this.breed;
  return ret;
}

Or, using ES6 template strings :

Dog.prototype.toString = function dogToString() {
  return `Dog ${this.name} is a ${this.sex} ${this.color} ${this.breed}`;
}

With the preceding code in place, any time theDog is used in a string context, JavaScript automatically calls the dogToString() function, which returns the following string:

"Dog Gabby is a female chocolate Lab"

使用 `toString()` to detect object class

toString() can be used with every object and (by default) allows you to get its class.

To use the Object.prototype.toString() with every object, you need to call Function.prototype.call() or Function.prototype.apply() on it, passing the object you want to inspect as the first parameter (called thisArg ).

const toString = Object.prototype.toString;
toString.call(new Date);    // [object Date]
toString.call(new String);  // [object String]
toString.call(Math);        // [object Math]
// Since JavaScript 1.8.5
toString.call(undefined);   // [object Undefined]
toString.call(null);        // [object Null]

使用 toString() in this way is unreliable; objects can change the behavior of Object.prototype.toString() by defining a Symbol.toStringTag property, leading to unexpected results. For example:

const myDate = new Date();
Object.prototype.toString.call(myDate);     // [object Date]
myDate[Symbol.toStringTag] = 'myDate';
Object.prototype.toString.call(myDate);     // [object myDate]
Date.prototype[Symbol.toStringTag] = 'prototype polluted';
Object.prototype.toString.call(new Date()); // [object prototype polluted]

规范

规范
ECMAScript (ECMA-262) The definition of 'Object.prototype.toString' in that specification.

浏览器兼容性

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request. 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
`toString()`	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 Yes

在此页

句法

返回值

描述

参数

范例

Overriding the default `toString` 方法

使用 `toString()` to detect object class

规范

浏览器兼容性

图例

另请参阅

元数据

相关话题

在此页

句法

返回值

描述

参数

范例

Overriding the default toString 方法

使用 toString() to detect object class

规范

浏览器兼容性

图例

另请参阅

相关话题

Overriding the default `toString` 方法

使用 `toString()` to detect object class