Why doesn't it print a number?

• 0

  let salaries= {
          John:100,
          Ann:160,
          Pete:130,
      }
      let sum;
      let summ=(obj)=>{
          for(key in obj) {
              sum+=obj[key]; 
          }
      }
  
      summ(salaries);
  console.log(typeof(sum));
  console.log(sum);

  
  
  Type writes: number
  And on the output: NaN
  
  Why?

  JavaScript Anonymous, Dec 7, 2020

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4 Answers
• 0
  Because sum initially contains undefined.
  
  
  
  Try this:
  
  let sum = 0;

  Grayson Clements

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• 0
  We need to initialize the variable sum.
  
  let sum = 0;

  Anonymous

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• 0
  The initial value of sum is not set.
  
  Well, the solution itself is not the best. Using an external variable in a function unnecessarily is bad manners.
  
  

  let summ = (obj) => {
  
    let sum = 0
  
    for (key in obj) {
  
      sum += obj[key]
  
    }
  
    return sum
  
  }
  
  let sum = summ(salaries)

  Anonymous

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• 0
  Rewrite the cycle like this and see.
  
  

  for (key in obj) {
  
      console.log(sum, obj[key])
  
      sum += obj[key];
  
    }

  
  
  Also read MDN what the for in loop outputs and how it differs from
  
  Object.keys ()
  
  And this is it
  
  https://www.oreilly.com/library/view / you-dont-know ...

  Anonymous

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