why is outer variable not available in if conditional

    function NumStuff(num) {
    this.num = num;
    this.multipleOfFour = function () {

        //if multiple of 4
        if (this.num % 4 === 0) {
            console.log(this.num + " is a multiple of Four");
            console.log("the structure of the given integer " + 
                        this.num + " is ");

            for (let i = 0; i < this.num; i++) {
                if (4 * i === this.num) { //why is this.num outside of 
                                          //lexical scope
                    console.log(this.num + " = " + i + " x 4");
                    break;
                }
            }
            //if not a multiple of 4
        } else {
            console.log(this.num + " isn't a multiple of 4 but here is the integer's structure:");
            let remainder = this.num % 4;
            let tempNum = this.num - remainder;
            for (let i = 0; i < tempNum; i++) {
                if (4 * i === tempNum) {
                    console.log(this.num + " = " + i + " x 4 + " + remainder);
                    break;
                }
            }
        }
    };
}

let num = prompt("Enter an integer:");
let n = new NumStuff(num);
n.multipleOfFour();

Say we enter 20 as our num. It passes through the multipleOfFour() and hits the first if conditional. This.num(20) % 4 is equal to 0 so it passes.Then we loop through i to find what number times 4 is equal to 20. This.num is in the scope of the for statement but not in the scope of the inner if conditional of the for statement. Why is that so?