add up each item in array code example

Example 1: add all elements in array javascript

console.log(
  [1, 2, 3, 4].reduce((a, b) => a + b, 0)
)
console.log(
  [].reduce((a, b) => a + b, 0)
)

Example 2: javascript add 1 to each element in array

var numberarr2 = numberarr.map( function(value) { 
    return value - 1; 
} );