A programming language is said to have first-class functions when functions in that language are treated like any other variable.

This means, in such a language, a function can be passed as an argument to other functions, returned by another function, and assigned as a value to a variable.

As a result, they exist in Javascript.

As a variable

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1const welcome = () => console.log('hello world');
2welcome(); //prints 'hello world'

As an Argument

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1function CallPrintFunction (func) {
2
3  if (typeof func === 'function') func(); 
4
5}

The CallPrintFunction function would accept a function as a parameter and call it. Kindly note in javascript it’s better to double check if the argument is a function using typeof before calling it.

To use the above CallPrintFunction simply do the following

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1const welcome = () => console.log('hello world');
2CallPrintFunction(welcome);
3
4// prints 'hello world'

Returned from another function

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1function ReturnWelcome() {
2
3return function welcome() { console.log('hello world');}
4
5}

To use the ReturnWelcome function above i.e. call the function returned simply do the following

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1ReturnWelcome()();

This one is pretty interesting since you can leverage closures to even enhance your returned function. Making another short post on closures soon I promise it would be straight forward.

That’s it Guys! . thanks for going through.