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JavaScript every() method

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JavaScript every method, how it works and why you need it

25 Nov, 2020 · 1 min read

Yesterday we had a look at the JavaScript some() method, and today we will focus on its brother every().

The main difference between the two:

  • some(): If at least one matches
  • every(): All must match!

Both of them will give us a boolean value back.

Using the Javascript every() method

Let's start by creating an array of items.

const items = [
  { name: 'T-shirt plain', price: 9 },
  { name: 'T-shirt print', price: 20 },
  { name: 'Jeans', price: 30 },
  { name: 'Cap', price: 5 },
];

We want to check if all the items have a name.

const haveNames = items.every((item) => {
  return item.name;
});

// Returns true

If we now remove the name on our item, it will return false.

Let's take a more accurate example. We have a list of users with temperatures. We want to see if everyone is under 37.8, or else someone potentially risks Covid-19.

const users = [
  { name: 'Bob', temperature: 36.3 },
  { name: 'Sarah', temperature: 37.9 },
  { name: 'Billy', temperature: 36.9 },
];

const temperature = users.every((user) => {
  return user.temperature < 37.8;
});

// Returns false

Whoops! Sarah has a high temperature, so we get a false back, which means we need to do something.

I hope this shows how one line can beat an array to loop over people.

The syntax for every is as follows:

const new = original.every(function(value));

Inside our function, we can check on specific properties the value has.

And remember:

Stay safe

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