---
lang: ja-jp
breaks: true
---
# TypeScript で null undefined empty を否定した場合の動作　2021-05-15

'use strict';

if (!null)
{
    console.log("not null.");
}
if (null != true)
{
    console.log("null is not true.");
}
if (!"")
{
    console.log("not emply.");
}
// ↓compile error.
//if ("" != true)
//{
//    console.log("emply is not true.");
//}
if (!undefined)
{
    console.log("not undefined.");
}
if (undefined != true)
{
    console.log("undefined is not true.");
}

console.log("exit.");

$ ts-node null_test.ts 
not null.
null is not true.
not emply.
not undefined.
undefined is not true.
exit.

###### tags: `TypeScript` `null` `undefined` `empty` `ts-node`