The difference between String.prototype.toString() and Object.prototype.toString() in JavaScript! ! !
tags: JavaScript String js front end jquery
Object.prototype.toString()
Let's first look at a small example:
function Dog(name) {
this.name = name;
}
const dog1 = new Dog('boy');
Dog.prototype.toString = function dogToString() {
return '' + this.name;
}
console.log(dog1.toString());
// Output: "boy"
Every object has a toString() method, which is automatically called when the object is represented as a text value, or when an object is referenced in an expected string manner. By default, the toString() method is inherited by every Object object. If this method is not covered in the custom object, toString() returns "[object type]", where type is the type of the object.
use
- Use toString() to detect object type
You can get the type of each object through toString(). In order for each object to be detected by Object.prototype.toString(), it needs to be called in the form of Function.prototype.call() or Function.prototype.apply(), passing the object to be checked as the first parameter, Called thisArg.
var 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]
String.prototype.toString()
The following example outputs the string value of a String object:
var x = new String("Hello world");
alert(x.toString()) // output "Hello world"
the difference:
The String object overrides the toString method of the Object object; it does not inherit Object.toString(). For String objects, the toString method returns the string form of the object, which is the same as the return value of the String.prototype.valueOf() method.
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