“Undefined” In Javascript

Michael S
1 min readFeb 18, 2019

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“undefined” through example with a simple function

Simple example when a function parameter is recognized as “undefined” in JS.

Function

function undefinedOrNot(value) {
if (value === undefined) {
return 'error';
} else {
return value;
}
}
  1. Input undefined
undefinedOrNot(undefined)
// "error"

2. Input no parameter

undefinedOrNot()
// "error"

3. Input a string parameter

ensure("I am string")
// "I am string"

I am blogging what I’ve learned to find later here for myself. If you happened to read this shit and there is wrong information, it would be appreciated to add a comment below.

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