Number( )
可以將其他的類型轉換成"number"
字串裡面是一個合法的數字，則轉換對應的數字
字串裡面是空白，則轉換成數字0

留意以下狀況!!
字串裡面不是合法的數字，則轉換為NaN
null，則轉換為0
undefined，則轉換為NaN

let a = "123";
a = Number(a);

let b = "english";
b = Number(b);

let c = "32px";
c = Number(c);

let d = "    ";
d = Number(d);

let e = true;
e = Number(e);

let f = null;
f = Number(f);

let g = undefined;
g = Number(g);

console.log(a, typeof b, b, c, d, e, f, g);

//輸出      123 "number" NaN  NaN  0  1  0  NaN

接續來介紹，類似但是結果不同
parseInt( )
將字串轉換成一個整數
parseInt解析的時候，從左至右讀取字串，直到讀取字串裡面所有的整數
字串的左邊第一個不是數字，則轉換為NaN

let a = "32px";
a = parseInt(a);
console.log(a, typeof a);

//輸出 32 "number"

let b = "3.14159265359";
b = parseInt(b);
console.log(b, typeof b);

//輸出 3 "number"

let c = "hello77";
c = parseInt(c);
console.log(c, typeof c);

//輸出 NaN "number"

參考mdn文件
https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Number