JavaScript Function bind()

// object definition
const student1 = {
  name: "Jack",
  grade: "5",
  introduction: function () {
    console.log(this.name + "studies in grade" + this.grade + ".");
  },
};

// object definition
const student2 = {
  name: "Jimmy ",
  grade: " 6",
};

// the object student2 is borrowing introduction method from student1
let result= student1.introduction.bind(student2);

// invoking introduction() function
result();

// Output:
// Jimmy studies in grade 6.

bind() Syntax

The syntax of the bind() method is:

func.bind(thisArg, arg1, ... argN)

Here, func is a function.

bind() Parameters

The bind() can take two parameters:

• thisArg - The value provided as this parameter for func.
• arg1, ... argN (optional) - The value of arguments present inside func.

bind() Return Value

• Returns a copy of the given function with the specified this value, and initial arguments (if provided).

Example 1: Using bind() Method

// object definition
const student1 = {
  name: "Jack",
  grade: "5",
  introduction: function () {
    console.log(this.name + "studies in grade" + this.grade + ".");
  },
};

// object definition
const student2 = {
  name: "Jimmy ",
  grade: " 6",
};

// the object student2 is borrowing introduction method from student1
let result= student1.introduction.bind(student2);

// invoking result() function
result();  // Jimmy studies in grade 6.

Output

Jimmy studies in grade 6.

In the above example, we have defined two objects student1 and student2.

Since student2 doesn't have the introduction() method, we are borrowing it from student1 using the bind() function.

student1.introduction.bind(student2) returns the copy of introduction() and assigns it to result.

Example 2: Using bind() Method with two Parameters

// object definition
const student1 = {
  name: "Jack",
  introduction: function (score) {
    console.log(this.name + "scored " + score + " in an exam.");
  },
};

// object definition
const student2 = {
  name: "Jimmy ",
};

// passing two parameters student2 and '95'
let result = student1.introduction.bind(student2, 95);

// invoking result() function
result(); // Jimmy scored 95 in an exam.

Output

Jimmy scored 95 in an exam.

In the above example, we have passed two parameters thisArg and arg1 in bind().

The student2 object is passed as this parameter and 95 is passed as an argument for the score parameter.

Recommended Reading: JavaScript Function call()