how to use arguments object by js

Question

today,i want to get a sum number,but get a wrong number.

function fun(a,b,c){
  var l = arguments.length;
  console.log('length'+l);
  for(var i=0;i<l;i++){
    var sum;
    console.log(arguments[i]);
    sum= sum+arguments[i];
  }
  return sum;
}
var p= fun(1,2,3);
console.log(p);

p is 'NaN'

if change the fun(1,2,3) to fun(1,2,3,4,5),is there some differences?

Denys Séguret · Accepted Answer · 2015-07-20 15:43:46Z

4

The problem is you're not initializing sum, so you're adding to undefined the first time (undefined+1 gives NaN), then to NaN.

Change

for(var i=0;i<l;i++){
 var sum;
 console.log(arguments[i]);
 sum= sum+arguments[i];
}

to

var sum = 0;
for(var i=0;i<l;i++){
 console.log(arguments[i]);
 sum= sum+arguments[i];
}

Note that the var sum declaration is hoisted to the start of the function.

edited Jul 20, 2015 at 15:43

answered Jul 20, 2015 at 15:42

Denys Séguret

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2 Comments

Denys Séguret Over a year ago

@dukegod What do you mean ? There's no closure here.

hui Over a year ago

if i put var sum declaration inside 'for function',why there console 'NAN'.

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