some-every-practice

Let's practice using every and some!

Complete the functions inside of the every.js and some.js files so that the associated tests pass. You should only need to use some and every.

Tests can be run with jasmine-node .

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.some()

Some works by taking a function that returns true or false. If any of the elements in the array return true, then the entire statement returns true. Another way to think of some is that it checks for any value passes the test provided by the function.

Check out the docs.

Example

Imagine we have a group of users that are the following age who have all signed up for some sort of tour through our application.

var ages = [23,32,17,19,34];

We want to show an ad that displays delicious beer but don't want to do so if any of the group members are under 21. A function that just tests whether or not a value is less than 21 might look like this:

var lessThan21 = function (age) {
  return (age < 21)
};

// lessThan21(20) >> true
// lessThan21(30) >> false

We can use some to check if any of the values are less than 21 in just one go:

var anyLessThan21 = function (ages) {
  return ages.some(function (age) {
    return age < 21;
  });
};

// anyLessThan21(ages) >> true

If the function returns true, we will not show the ad.

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.every()

Some works by taking a function that returns true or false. If all of the elements in the array return true, only then will the entire statement return true.

Check out the docs.

Example

Consider the same example above, but instead of checking if any of the values are less than 21, we want to check that all of the values are equal to or greater than 21. A simple function to return if a single age is 21 or older would look like:

var twentyOneOrAbove = function (age) {
  return age >= 21;
};

// twentyOneOrAbove(20) >> false
// twentyOneOrAbove(30) >> true

We can use every to check for all the values in the array.

var all21OrAbove = function (ages) {
  return ages.every(function (age) {
    return age >= 21;
  });
};

// all21OrAbove(ages) >> false