How to find the sum of an array of numbers
In Lisp, this'd be exactly the job for reduce. You'd see this kind of code:
(reduce #'+ '(1 2 3)) ; 6Fortunately, in JavaScript, we also have reduce! Unfortunately, + is an operator, not a function. But we can make it pretty! Here, look:
const sum = [1, 2, 3].reduce(add,0); // with initial value to avoid when the array is emptyfunction add(accumulator, a) { return accumulator + a;}console.log(sum); // 6Isn't that pretty? :-)
Even better! If you're using ECMAScript 2015 (aka ECMAScript 6), it can be this pretty:
const sum = [1, 2, 3].reduce((partial_sum, a) => partial_sum + a,0); console.log(sum); // 6
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 : nconsole.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);