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Quick Tip: JavaScript Partially Applied Functions

Say we have the following function:

<code class="javascript">
function increaseBy(x){
  return function(y){
    return x + y;
  }
}

We can use this function to create new, higher order functions that increase a number by a certain value.

for example:

<code class="javascript">
var incByThree = increaseBy(3);

gives us a function we can then use later in our code as such:

<code class="javascript">
incByThree(4);
//returns 7

incByThree(5);
//returns 8

We can also create multiple higher-order functions and have each of them use a different x value;

<code class="javascript">
var incByThree = increaseBy(3);
var incByFour = increaseBy(4);

incByThree(6);
//returns 9
incbyFour(6);
//returns 10