Javascript call() & apply() vs bind()?

我已经知道apply和call是类似的函数，它们设置this(函数的上下文)。

区别在于我们发送参数的方式(manual vs array)

问题:

但是什么时候应该使用bind()方法呢?

var obj = {
  x: 81,
  getX: function() {
    return this.x;
  }
};

alert(obj.getX.bind(obj)());
alert(obj.getX.call(obj));
alert(obj.getX.apply(obj));

jsbin

当前回答

JavaScript调用()

const person = {
    name: "Lokamn",
    dob: 12,
    print: function (value,value2) {
        console.log(this.dob+value+value2)
    }
}
const anotherPerson= {
     name: "Pappu",
     dob: 12,
}
 person.print.call(anotherPerson,1,2)

JavaScript应用()

    name: "Lokamn",
    dob: 12,
    print: function (value,value2) {
        console.log(this.dob+value+value2)
    }
}
const anotherPerson= {
     name: "Pappu",
     dob: 12,
}
 person.print.apply(anotherPerson,[1,2])

**call和apply函数是不同的，调用单独的参数，但应用数组如:(1、2、3) **

JavaScript绑定()

    name: "Lokamn",
    dob: 12,
    anotherPerson: {
        name: "Pappu",
        dob: 12,
        print2: function () {
            console.log(this)
        }
    }
}

var bindFunction = person.anotherPerson.print2.bind(person)
 bindFunction()

2020-03-14 11:56:32

其他回答

我之前创建了函数对象、函数调用、call/apply和bind之间的比较:

.bind允许您现在设置this值，同时允许您在将来执行该函数，因为它返回一个新的函数对象。

2019-02-06 20:42:05

它们都将其附加到函数(或对象)中，区别在于函数调用(见下文)。

Call将此附加到函数中并立即执行函数:

var person = {  
  name: "James Smith",
  hello: function(thing) {
    console.log(this.name + " says hello " + thing);
  }
}

person.hello("world");  // output: "James Smith says hello world"
person.hello.call({ name: "Jim Smith" }, "world"); // output: "Jim Smith says hello world"

Bind将它附加到函数中，需要像这样单独调用:

var person = {  
  name: "James Smith",
  hello: function(thing) {
    console.log(this.name + " says hello " + thing);
  }
}

person.hello("world");  // output: "James Smith says hello world"
var helloFunc = person.hello.bind({ name: "Jim Smith" });
helloFunc("world");  // output: Jim Smith says hello world"

或者像这样:

...    
var helloFunc = person.hello.bind({ name: "Jim Smith" }, "world");
helloFunc();  // output: Jim Smith says hello world"

Apply类似于call，只是它接受一个类似数组的对象，而不是一次列出一个参数:

function personContainer() {
  var person = {  
     name: "James Smith",
     hello: function() {
       console.log(this.name + " says hello " + arguments[1]);
     }
  }
  person.hello.apply(person, arguments);
}
personContainer("world", "mars"); // output: "James Smith says hello mars", note: arguments[0] = "world" , arguments[1] = "mars"

2015-08-10 14:50:45

这里有一篇很好的文章来说明bind()、apply()和call()之间的区别，总结如下。

bind() allows us to easily set which specific object will be bound to this when a function or method is invoked. // This data variable is a global variable var data = [ {name:"Samantha", age:12}, {name:"Alexis", age:14} ] var user = { // local data variable data :[ {name:"T. Woods", age:37}, {name:"P. Mickelson", age:43} ], showData:function (event) { var randomNum = ((Math.random () * 2 | 0) + 1) - 1; // random number between 0 and 1 console.log (this.data[randomNum].name + " " + this.data[randomNum].age); } } // Assign the showData method of the user object to a variable var showDataVar = user.showData; showDataVar (); // Samantha 12 (from the global data array, not from the local data array) /* This happens because showDataVar () is executed as a global function and use of this inside showDataVar () is bound to the global scope, which is the window object in browsers. */ // Bind the showData method to the user object var showDataVar = user.showData.bind (user); // Now the we get the value from the user object because the this keyword is bound to the user object showDataVar (); // P. Mickelson 43 bind() allow us to borrow methods // Here we have a cars object that does not have a method to print its data to the console var cars = { data:[ {name:"Honda Accord", age:14}, {name:"Tesla Model S", age:2} ] } // We can borrow the showData () method from the user object we defined in the last example. // Here we bind the user.showData method to the cars object we just created. cars.showData = user.showData.bind (cars); cars.showData (); // Honda Accord 14 One problem with this example is that we are adding a new method showData on the cars object and we might not want to do that just to borrow a method because the cars object might already have a property or method name showData. We don’t want to overwrite it accidentally. As we will see in our discussion of Apply and Call below, it is best to borrow a method using either the Apply or Call method. bind() allow us to curry a function Function Currying, also known as partial function application, is the use of a function (that accept one or more arguments) that returns a new function with some of the arguments already set. function greet (gender, age, name) { // if a male, use Mr., else use Ms. var salutation = gender === "male" ? "Mr. " : "Ms. "; if (age > 25) { return "Hello, " + salutation + name + "."; }else { return "Hey, " + name + "."; } } We can use bind() to curry this greet function // So we are passing null because we are not using the "this" keyword in our greet function. var greetAnAdultMale = greet.bind (null, "male", 45); greetAnAdultMale ("John Hartlove"); // "Hello, Mr. John Hartlove." var greetAYoungster = greet.bind (null, "", 16); greetAYoungster ("Alex"); // "Hey, Alex." greetAYoungster ("Emma Waterloo"); // "Hey, Emma Waterloo." apply() or call() to set this value The apply, call, and bind methods are all used to set the this value when invoking a method, and they do it in slightly different ways to allow use direct control and versatility in our JavaScript code. The apply and call methods are almost identical when setting the this value except that you pass the function parameters to apply () as an array, while you have to list the parameters individually to pass them to the call () method. Here is one example to use call or apply to set this in the callback function. // Define an object with some properties and a method // We will later pass the method as a callback function to another function var clientData = { id: 094545, fullName: "Not Set", // setUserName is a method on the clientData object setUserName: function (firstName, lastName) { // this refers to the fullName property in this object this.fullName = firstName + " " + lastName; } }; function getUserInput (firstName, lastName, callback, callbackObj) { // The use of the Apply method below will set the "this" value to callbackObj callback.apply (callbackObj, [firstName, lastName]); } // The clientData object will be used by the Apply method to set the "this" value getUserInput ("Barack", "Obama", clientData.setUserName, clientData); // the fullName property on the clientData was correctly set console.log (clientData.fullName); // Barack Obama Borrow functions with apply or call Borrow Array methods Let’s create an array-like object and borrow some array methods to operate on the our array-like object. // An array-like object: note the non-negative integers used as keys var anArrayLikeObj = {0:"Martin", 1:78, 2:67, 3:["Letta", "Marieta", "Pauline"], length:4 }; // Make a quick copy and save the results in a real array: // First parameter sets the "this" value var newArray = Array.prototype.slice.call (anArrayLikeObj, 0); console.log (newArray); // ["Martin", 78, 67, Array[3]] // Search for "Martin" in the array-like object console.log (Array.prototype.indexOf.call (anArrayLikeObj, "Martin") === -1 ? false : true); // true Another common case is that convert arguments to array as following // We do not define the function with any parameters, yet we can get all the arguments passed to it function doSomething () { var args = Array.prototype.slice.call (arguments); console.log (args); } doSomething ("Water", "Salt", "Glue"); // ["Water", "Salt", "Glue"] Borrow other methods var gameController = { scores :[20, 34, 55, 46, 77], avgScore:null, players :[ {name:"Tommy", playerID:987, age:23}, {name:"Pau", playerID:87, age:33} ] } var appController = { scores :[900, 845, 809, 950], avgScore:null, avg :function () { var sumOfScores = this.scores.reduce (function (prev, cur, index, array) { return prev + cur; }); this.avgScore = sumOfScores / this.scores.length; } } // Note that we are using the apply () method, so the 2nd argument has to be an array appController.avg.apply (gameController); console.log (gameController.avgScore); // 46.4 // appController.avgScore is still null; it was not updated, only gameController.avgScore was updated console.log (appController.avgScore); // null Use apply() to execute variable-arity function

的数学。Max是变量函数的一个例子，

// We can pass any number of arguments to the Math.max () method
console.log (Math.max (23, 11, 34, 56)); // 56

但是如果我们有一个数字数组要传递给Math.max呢?我们不能这样做:

var allNumbers = [23, 11, 34, 56];
// We cannot pass an array of numbers to the the Math.max method like this
console.log (Math.max (allNumbers)); // NaN

这就是apply()方法帮助我们执行可变函数的地方。与上述方法不同，我们必须使用apply()传递数字数组，如下所示:

var allNumbers = [23, 11, 34, 56];
// Using the apply () method, we can pass the array of numbers:
console.log (Math.max.apply (null, allNumbers)); // 56

2016-04-08 06:45:25

bind:它将函数与所提供的值和上下文绑定，但不执行函数。要执行函数，需要调用函数。

调用:它使用提供的上下文和参数执行函数。

apply:它使用提供的上下文和执行函数参数作为数组。

2017-11-22 17:31:46