js中判断是否为空

if (variable === null || variable === undefined) {
    console.log('变量为空');
}

if (typeof variable === 'string' && variable.trim() === '') {
    console.log('变量为空字符串');
}

if (Array.isArray(variable) && variable.length === 0) {
    console.log('变量为空数组');
}

if (typeof variable === 'object' && Object.keys(variable).length === 0) {
    console.log('变量为空对象');
}

function isEmpty(variable) {
    if (variable === null || variable === undefined) {
        return true;
    }
    if (typeof variable === 'string' && variable.trim() === '') {
        return true;
    }
    if (Array.isArray(variable) && variable.length === 0) {
        return true;
    }
    if (typeof variable === 'object' && Object.keys(variable).length === 0) {
        return true;
    }
    return false;
}

// 使用示例
console.log(isEmpty(null)); // true
console.log(isEmpty(undefined)); // true
console.log(isEmpty('')); // true
console.log(isEmpty([])); // true
console.log(isEmpty({})); // true
console.log(isEmpty('Hello')); // false
console.log(isEmpty([1, 2, 3])); // false
console.log(isEmpty({ a: 1 })); // false

if (typeof variable === 'number' && isNaN(variable)) {
    console.log('变量为NaN');
}