JavaScript (Node.js), 2623 bytes
n=>eval([...n].join`+`)
Takes input as a string
JavaScript (Node.js) , 26 bytes
n=>eval([...""+n].join`+`)
Takes input as a number, doesn't work if the number is too large for JavaScript to stringify naturally
JavaScript (Node.js), 23 bytes
n=>eval([...n].join`+`)
Takes input as a string
JavaScript (Node.js) , 26 bytes
n=>eval([...""+n].join`+`)
Takes input as a number, doesn't work if the number is too large for JavaScript to stringify naturally