如何从JavaScript中的内部函数访问外部函数变量？

Question

Am just getting the ropes of JS Fundamentals, bear with me.

Following is the code :

function FuncWithMathOps(x){
var x=x;

console.log("Value of x : "+x);

var SUM = function(x){
    var x=x;

    console.log("Value of x : "+x);
    console.log("Value of this.x : "+this.x);
}

var MUL = function(x){
    var x=x;

    console.log("Value of x : "+x);
    console.log("Value of this.x : "+this.x);
}

return {
    SUM:SUM,
    MUL:MUL
};

}

Both external function and inner functions variable names are same ie, x & y . How do i access external function FuncWithMathOps variables from inner functions SUM & MUL ?

Answer 1

You can create a variable self which persist the reference to this , which can be used later.

 function FuncWithMathOps(x) { this.x = x; var self = this; console.log("Value of x : " + x); var SUM = function(x) { console.log("Value of x : " + x); console.log("Value of this.x : " + self.x); return x + self.x; } return { SUM: SUM }; } var fn = new FuncWithMathOps(10); console.log(fn.SUM(5)) 

You can also use .bind()

 function FuncWithMathOps(x) { this.x = x; console.log("Value of x : " + x); var SUM = function(x) { console.log("Value of x : " + x); console.log("Value of this.x : " + this.x); return x + this.x; } return { SUM: SUM.bind(this) }; } var fn = new FuncWithMathOps(10); console.log(fn.SUM(5))