Using the filter array helper in ES6

ES6 comes with a number of helper methods that can be applied to arrays. One of these is called filter which can filter out various elements from an array and add those elements to a new array. If you’re familiar with C# and LINQ then the filter function is very similar to the Where and ToList LINQ extension methods.

Let’s see an example:

We have the following group of programmers:

let programmers = [
  	 {"name":"John","age":20,"language":"C#"},
     {"name":"Mary","age":24,"language":"Java"},
     {"name":"Jane","age":25,"language":"C++"},
     {"name":"Peter","age":22,"language":"JavaScript"},
     {"name":"Fred","age":21,"language":"C++"},
     {"name":"Sophie","age":28,"language":"C#"},
     {"name":"James","age":27,"language":"Java"},
     {"name":"Charlotte","age":26,"language":"Java"},
]

Say that we want to find all programmers of 25 years of age and above. Here’s how we can do it using the filter array helper:

let above25 = programmers.filter(function(prog) {
  return prog.age >= 25
});

Filter accepts a function which in turn operates on a single member of the array which the filter is applied to. Filter iterates through each member in the array and calls the function that was provided to it. The function must return a value otherwise the result, “above25” in this case will be an empty array. If the value of the argument “prog” fulfils the boolean condition in the filter function it is added to the above25 array:

[{"name":"Jane","age":25,"language":"C++"},{"name":"Sophie","age":28,"language":"C#"},{"name":"James","age":27,"language":"Java"},{"name":"Charlotte","age":26,"language":"Java"}]

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