检查null，empty或undefined angularjs [英] check null,empty or undefined angularjs

问题描述

我正在使用angularjs创建一个项目.我有像这样的变量

I am creating a project using angularjs.I have variable like

$scope.test = null
$scope.test = undefined
$scope.test = ""

我想在一种情况下检查所有null，undefined和empty值

I want to check all null,undefined and empty value in one condition

推荐答案

只需使用-

if(!a) // if a is negative,undefined,null,empty value then...
{
    // do whatever
}
else {
    // do whatever
}

之所以起作用，是因为javascript中===与===的区别在于，它会将某些类型的值转换为其他类型的相等"值以检查是否相等，而===则相反，后者仅检查这些值是否相等.因此，基本上==运算符知道将未定义的"，null转换为假值.正是您所需要的.

this works because of the == difference from === in javascript, which converts some values to "equal" values in other types to check for equality, as opposed for === which simply checks if the values equal. so basically the == operator know to convert the "", null, undefined to a false value. which is exactly what you need.

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