jquery - $(select).val().length of null 给出错误

Question

我的表单中有一个选择对象，使用 Bootstrap-select.js 插件设置样式。当我初始化选择框并尝试获取它的值时，它是 null ，直到我选择一个选项。在我的脚本中我使用:-

$(select).val().length

但是，当 $(select).val() 为 null 时，会出现错误。我真的很想得到一个0。

我该怎么做？

Answer 1

尝试:-

($(select).val() || '').length

Logical Operators

Logical operators are typically used with Boolean (logical) values. When they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value.

Examples of expressions that can be converted to false are:

• null
• NaN
• 0
• empty string ("")
• NaN
• undefined

演示

var length = ($('select').val() || '').length;

console.log('length: ' + length);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<select>

<select>