Using the every array helper in ES6

ES6 comes with a number of helper methods that can be applied to arrays. One of these is called every which returns true if all elements in an array fulfil the specified condition and false otherwise. If you’re familiar with C# and LINQ then the every function is very similar to the All LINQ extension method.

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"},
]

We want to find out if everyone has turned 18. This is how we can achieve that using the every function:

let allOver18 = programmers.every(function(prog) {
  return prog.age >= 18
})

Every accepts a function which in turn operates on a single member of the array which every is applied to. Every 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, “allOver18” will always be false due to the null returned from the function. Null is a falsy JS value so allOver18 will also be false. If all array elements fulfil the condition then allOver18 will be true, which is in fact the case in our example.

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