js中typeof的用法

typeof variable

typeof (expression)

console.log(typeof undefined); // "undefined"
console.log(typeof true);      // "boolean"
console.log(typeof 123);       // "number"
console.log(typeof "hello");   // "string"
console.log(typeof 123n);      // "bigint"
console.log(typeof Symbol());  // "symbol"
console.log(typeof null);      // "object"（注意这是一个历史遗留问题）
console.log(typeof {});        // "object"
console.log(typeof []);        // "object"
console.log(typeof function(){}); // "function"

function addNumbers(a, b) {
    if (typeof a !== 'number' || typeof b !== 'number') {
        throw new TypeError('Both arguments must be numbers');
    }
    return a + b;
}

if (value === null) {
    // value 是 null
}