changing the constructor of an object does not work when done through a variable

Question

I am having difficulty understand this behavior in Javascript. I am trying to assign a value to this.val, when I try to assign it a value using a variable, it does not assign successfully...

Example 1)

class TestVariableAssignment {
    constructor() {
        this.val = null;
    }

     assign() {
        let value = this.val;
        value = 5;
        console.log(this.val); // null
    }
}

const testVariableAssignment = new TestVariableAssignment();

testVariableAssignment.assign();

Example 2) this one seems to assign this.val a value correctly though ....

class TestVariableAssignment {
    constructor() {
        this.val = null;
    }

    assign() {
        this.val = 5;
        console.log(this.val); // 5
    }
     
}

const testVariableAssignment = new TestVariableAssignment();

testVariableAssignment.assign();

Why does this occur? Can someone why Example 1 does not work but example 2 does? Why can I not update this.val while using a variable?