Author: John Au-Yeung

Checking if an array includes a value is something that we’ve to do often in a JavaScript app.

In this article, we’ll look at how to check if an array includes a given value in JavaScript.

Array.prototype.includes

The includes method is a method that’s included with the array instance.

It takes a value and compares it with === to check if an element is included.

For instance, we can write:

console.log(['apple', 'orange', 'grape'].includes('orange'));

If it’s included, then it returns true .

Otherwise, it returns false .

Array.prototype.indexOf

We can also use the indexOf method of an array instance to check if it includes a given element.

It also uses === for comparison.

And it returns the index of the first instance of an item if it exists.

Otherwise, it returns -1.

To use it, we write:

console.log(['apple', 'orange', 'grape'].indexOf('orange') >= 0);

Write Our Own

We can write our own function to search for a value.

For instance, we can write:

function contains(a, obj) {
  let i = a.length;
  while (i--) {
    if (a[i] === obj) {
      return true;
    }
  }
  return false;
}

console.log(contains(['apple', 'orange', 'grape'] , 'orange'));

We create the contains function that uses a while loop to search for an item.

If a[i] has the same value as obj then we return true .

If we loop through the whole a array and didn’t find anything that matches, then we return false .

Array.prototype.some

The some method is another array instance method that comes with JavaScript arrays.

It lets us pass in a callback to check if any items match the given condition.

For instance, we can write:

const items = [{
  a: '1'
}, {
  a: '2'
}, {
  a: '3'
}]

console.log(items.some(item => item.a === '3'))

We have an items array that has a bunch of objects.

And we call items.some with a callback to check if any items entry with a property equal to 3 exists.

some returns true if an item that matches the given condition exists and false otherwise.

Conclusion

There’re many ways to find if an array item exists in JavaScript.

A UNIX timestamp is the number of seconds since January 1, 1970 midnight UTC.

It’s often used so that we can do calculations with time easily.

In this article, we’ll look at how to get the UNIX timestamp from a date object in JavaScript.

The + Operator

We can use the + operator to convert the date object right to a UNIX timestamp.

For instance, we can write:

+new Date()

The + operator before the date object triggers the valueOf method in the Date object to return the timestamp as a number.

The getTime Method

We can call getTime to do the same thing.

For instance, we can write:

new Date().getTime()

to return the UNIX timestamp of a date.

Date.now Method

Date.now is a static method of the Date constructor that lets us get the current date-times timestamp.

For instance, we can write:

Date.now()

The timestamp is returned in milliseconds, so we have to divide it by 1000 and round it to get the timestamp in seconds.

To do that, we write:

Math.floor(Date.now() / 1000)

Math.floor rounds the number down to the nearest integer.

We can also round it with Math.round by writing:

Math.round(new Date().getTime() / 1000);

Number Function

The Number function is a global function that lets us convert a non-number object or primitive value to a number.

And we can use it to convert a date to a timestamp.

To do that, we write:

Number(new Date())

Then we get the timestamp in seconds returned since it triggers the valueOf method of the Date instance like the + operator.

Lodash _.now Method

Lodash also has a now method that returns the current timestamp.

To use it, we write:

_.now();

It’ll also return the current date’s timestamp.

Conclusion

There’re many ways to get the timestamp of the current date and time or the date-time that we want with JavaScript.