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圆括号运算符 - JavaScript | MDN

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圆括号运算符 ( ) 用于控制表达式中的运算优先级。

console.log(1 + 2 * 3); // 1 + 6
// Expected output: 7

console.log(1 + 2 * 3); // 1 + 6
// Expected output: 7

console.log((1 + 2) * 3); // 3 * 3
// Expected output: 9

console.log(1 * 3 + 2 * 3); // 3 + 6
// Expected output: 9

圆括号运算符由一对圆括号组成，包裹表达式和子表达式用来覆盖常规的运算符优先级，达到低优先级的表达式比高优先级的表达式更早运算。

下面的代码展示了加法运算先于乘法运算的情况。

const a = 1;
const b = 2;
const c = 3;

// 默认优先级
a + b * c; // 7
// 默认运算顺序同下
a + (b * c); // 7

// 现在优先考虑乘法之前的加法
(a + b) * c; // 9

// 这相当于
a * c + b * c; // 9

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