JavaScript Iterators #

Called on arrays to return values.

Methods #

.filter() #

Returns an array after filtering out some elements.

Callback function used should return true or false. true elements are added to the returned array.

const someArr = [1, 2, 3]

const newArr = someArr.filter(
    num => {
        return num > 1;
    }
)

.findIndex() #

Find the index of an element in an array based on some condition. Returns the first element that is true.

const someArr = [1, 2, 3]

const newArr = someArr.findIndex(
    num => {
        return num > 2;
    }
)

If nothing matches, a -1 is returned.

.forEach() #

Run the same code on each element of an array.

const someArr = [1, 2, 3]

someArr.forEach(
    function(arrItem) {
        console.log(arrItem * arrItem);
    }
)

Can also be expressed as an arrow function.

.map() #

Takes an array, returns an array.

const someArr = [1, 2, 3]; 

const squaredArr = someArr.map(
    number => { // number is a parameter
        return number * number 
    }
);

.reduce() #

Takes in array, returns a single value.