如何從動態值中獲取第一個值

Question

我想存儲總是變化的變量的第一個值。 我的想法是使用數組來存儲它。 還有其他方法可以實現嗎？

let arr = [];
function test() {
    let r;
    r = Math.random() * 100;        //emulate to get the value dynamically
    arr.push(r);
    return r;
}

alert(test());
alert(test());
alert(arr[0]);      //Always get the first value 

Answer 1

Here the variable 'res' is assigned to null initially and checked inside the function for null, if res === null you can store the first occurrence to it. 請注意 'let' 和 'var' 范圍

 var res = null; function test() { let r; r = Math.random() * 100; //emulate to get the value dynamically if(res === null) { res = r; } return r; } alert(test()); alert(test()); alert(res);