How to find the sum of an array of numbers
This'd be exactly the job for reduce
.
If you're using ECMAScript 2015 (aka ECMAScript 6):
const sum = [1, 2, 3].reduce((partialSum, a) => partialSum + a, 0);
console.log(sum); // 6
For older JS:
const sum = [1, 2, 3].reduce(add, 0); // with initial value to avoid when the array is empty
function add(accumulator, a) {
return accumulator + a;
}
console.log(sum); // 6
Isn't that pretty? :-)
Recommended (reduce with default value)
Array.prototype.reduce can be used to iterate through the array, adding the current element value to the sum of the previous element values.
console.log(
[1, 2, 3, 4].reduce((a, b) => a + b, 0)
)
console.log(
[].reduce((a, b) => a + b, 0)
)
Without default value
You get a TypeError
console.log(
[].reduce((a, b) => a + b)
)
Prior to ES6's arrow functions
console.log(
[1,2,3].reduce(function(acc, val) { return acc + val; }, 0)
)
console.log(
[].reduce(function(acc, val) { return acc + val; }, 0)
)
Non-number inputs
If non-numbers are possible inputs, you may want to handle that?
console.log(
["hi", 1, 2, "frog"].reduce((a, b) => a + b)
)
let numOr0 = n => isNaN(n) ? 0 : n
console.log(
["hi", 1, 2, "frog"].reduce((a, b) =>
numOr0(a) + numOr0(b))
)
Non-recommended dangerous eval use
We can use eval to execute a string representation of JavaScript code. Using the Array.prototype.join function to convert the array to a string, we change [1,2,3] into "1+2+3", which evaluates to 6.
console.log(
eval([1,2,3].join('+'))
)
//This way is dangerous if the array is built
// from user input as it may be exploited eg:
eval([1,"2;alert('Malicious code!')"].join('+'))
Of course displaying an alert isn't the worst thing that could happen. The only reason I have included this is as an answer Ortund's question as I do not think it was clarified.
Why not reduce? It's usually a bit counter intuitive, but using it to find a sum is pretty straightforward:
var a = [1,2,3];
var sum = a.reduce(function(a, b) { return a + b; }, 0);