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) )
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Without default value
You get a TypeError
console.log( [].reduce((a, b) => a + b) )
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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)
)
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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))
)
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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('+'))
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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.