Syntax Error: Invalid left-hand side in assignment when evaluating keys in object using for-in-loop JavaScript

Question

I have an object called sumMe containing several key/value pairs and a variable called total whose initial value is 0. I'm using a for... in loop to iterate through the keys of sumMe and if the value corresponding to a key is a number, I want to add it to total.

const sumMe = {
  hello: 'there',
  you: 8,
  are: 7,
  almost: '10',
  done: '!'
};
let total = 0;

for (let keys in sumMe ) {
  if (typeof(sumMe[keys]) = "number") {
    total + sumMe[keys]
  }
}

console.log(sumMe)

I get the following error when I try to evaluate it: Syntax Error: Invalid left-hand side in assignment

The expected total should equal 15. It currently reads "0" when correcting for the comparison operator changing "=" to "===" above.

Also, instead of `total + sumMe[keys]` (which does nothing), you may want to do `total += sumMe[keys]` — blex, Jul 01 '20 at 19:52
Note that `typeof` is an operator, not a function, so the parentheses are redundant. — Heretic Monkey, Jul 01 '20 at 19:55

score 2 · Accepted Answer · answered Jul 01 '20 at 19:52

2

The equality check is missing the second '='. And maybe you'd like to increase total, so change + to +=.

Write

for (let keys in sumMe ) {
  if (typeof(sumMe[keys]) == "number") {
    total += sumMe[keys]
  }
}

hth

answered Jul 01 '20 at 19:52

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Syntax Error: Invalid left-hand side in assignment when evaluating keys in object using for-in-loop JavaScript

1 Answers1