The reduce() method

reduce()

This is one of the most powerful JavaScript array methods because it applies a reducer function to each element of your array and returns a single output. The reducer function iterates through all elements in your array from left to right (in order) and returns the result of the previous element’s calculation. 

Thus, the final result is a single value. This single value is the function’s accumulated result after executing a reducer function for every array element.

```
// Syntax
myArray.reduce(callbackFn, initialValue)
```

For example:
```
let salaries = [100, 300, 500];
let salary = salaries.reduce((x, y) => x + y, 0);
console.log(salary);
```