Page 94 - JavaScript

In all versions of JavaScript, it is possible to iterate through the indices of an array using a
traditional C-style for loop.

var myArray = [1, 2, 3, 4];
for(var i = 0; i < myArray.length; ++i) {
var twoValue = myArray[i] * 2;
console.log("2 * value is: %d", twoValue);
}

It's also possible to use while loop:

var myArray = [1, 2, 3, 4],
i = 0, sum = 0;
while(i++ < myArray.length) {
sum += i;
}
console.log(sum);

Array.prototype.every

Since ES5, if you want to iterate over a portion of an array, you can use Array.prototype.every,
which iterates until we return false:

5

// [].every() stops once it finds a false result
// thus, this iteration will stop on value 7 (since 7 % 2 !== 0)
[2, 4, 7, 9].every(function(value, index, arr) {
console.log(value);
return value % 2 === 0; // iterate until an odd number is found
});

Equivalent in any JavaScript version:

var arr = [2, 4, 7, 9];
for (var i = 0; i < arr.length && (arr[i] % 2 !== 0); i++) { // iterate until an odd number is
found
console.log(arr[i]);
}

Array.prototype.some

Array.prototype.some iterates until we return true:

5

// [].some stops once it finds a false result
// thus, this iteration will stop on value 7 (since 7 % 2 !== 0)
[2, 4, 7, 9].some(function(value, index, arr) {
console.log(value);
return value === 7; // iterate until we find value 7
});

https://riptutorial.com/ 51