How to Find the Sum of Array of Integers in JavaScript?

Using `Array.prototype.reduce()`

Introduced in ES5, the `reduce()` method can help reduce an array to a single value (by applying a function against an accumulator and each value of the array). To sum an array of integers using `reduce()`, you can do the following:

```// ES5+
const integers = [-1, 2, 3, -4, 5];
const sum = integers.reduce(function (accumulator, value) {
return accumulator + value;
}, 0);

console.log(sum); // output: 5
```

The same code can be written in a shorter syntax using the arrow function (introduced in ES6). For example:

```// ES6+
const integers = [-1, 2, 3, -4, 5];
const sum = integers.reduce((accumulator, value) => accumulator + value, 0);

console.log(sum); // output: 5
```

Note that the `0` at the end is the initial value, and the `accumulator` holds the "reduced" value returned by the function in each iteration.

You may also use the `Array.prototype.reduceRight()` method. The difference between `reduce()` and `reduceRight()` is that the former goes through values left-to-right while the latter goes through values from right-to-left.

Using a Loop

You can simply use a loop to iterate over the entire array and sum the values. For example, to do that using a `for` loop, we can do the following:

```const integers = [-1, 2, 3, -4, 5];
let sum = 0;

for (let i=0; i < integers.length; i++) {
sum += integers[i];
}

console.log(sum); // output: 5
```

You can also refactor the `for` loop in a shorter syntax like so:

```const integers = [-1, 2, 3, -4, 5];
let sum = 0;

for (let i = 0; i < integers.length; sum += integers[i++]);

console.log(sum); // output: 5
```

Similarly, you may use other loops to sum all elements of an array of integers.

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