JavaScript Array — some() vs every() vs forEach()
July 27, 2019
This article explains the array’s
some(), every() and the forEach() method.
The some() method
The
some() method iterates through elements and checks if any value in the array satisfies a condition. The some() method accepts a boolean expression with the following signature:(element) => boolean
where the element is the current element in the array whose value is being checked
boolean denotes that the function returns a boolean value
Consider the following array of integers:
let arr = [1, 2, 3, 4, 5, 6, 7, 8];
We will be using the some() method to check if at least one element is even in the array.
arr.some((value)=> { return (value%2 == 0); });
Output:
true
As the array contains elements divisible by 2, so the
some() method returned true.
When tried some() method with the logic to find negative numbers
arr.some((value)=> { return (value < 0); });
The output is
false
As there are no numbers in the array that are negative.
The
some() method stops iterating as soon as the element is found which satisfies the required boolean expression.arr.some((value) => {
index++;
console.log(index);
return (value % 2 == 0);
});
Output is:
1 2 true
The every() method
Opposing to
some(), the every() method checks if each of the element in the array satisfies the boolean expression. If even a single value doesn't satisfy the element it returns false, else it returns true.let arr = [1, 2, 3, 4, 5, 6, 7, 8];arr.every((value)=> { return (value > 0); });
Since all of the values in the array
arr are positive, so the boolean expression satisfies for all of the values. We receive true as output.
With even a single value, not satisfying the boolean expression, we get the boolean output as
false.arr.every((value)=> { return (value == 5); });
Output:
false
The every() method stops iterating over the elements as soon as any value fails the boolean expression.
arr.every((value) => {
index++;
console.log(index);
return (value != 4);
});
Output:
1 2 3 false
The forEach() method
The
forEach() method, as the name suggests, is used to iterate over every element of the array and perform some desired operation with it.let arr = [1, 2, 3, 4, 5, 6, 7, 8];arr.forEach((value) => { console.log(value == 5); });
We get the output as:
false false false false true false false false
Nothing different here, just iterating each element with some operation (as required) on it.
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