converting a for loop to array filter

Question

This javascript code tries to use the array.filter for better performance instead of the for loop "I guess". Any way, the results are not the same, when it was expected to be. It tries to find out the names of students who are included in the searchWords array.
Any ideas why?thx

let searchWords = ['john','matt','marry'];
let students = ['matt','jack'];
let names = [];
for (let i = 0; i < searchWords.length; i++) {
   if (students.indexOf(searchWords[i]) !== -1) {
       names.push(searchWords[i]);
   }
}
console.log(names.length); // => 1 "correct"

names = [];
names = searchWords.filter(x => students.filter(y => students.indexOf(x) !== -1));
console.log(names.length); // => 3 "incorrect"

James Wesc · Accepted Answer · 2017-06-23 00:29:41Z

5

The filter line has essentially added another loop. It should be

names = searchWords.filter(x => students.indexOf(x) !== -1);

answered Jun 23, 2017 at 0:29

James Wesc

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3 Comments

RobG Over a year ago

I was just answering that… ;-)

David G Over a year ago

Wow javascript has changed since I last used it. Now we have let and lambda functions. Cool.

RobG Over a year ago

@0x499602D2—it always had lambda functions, the arrow syntax is new though (it sets this lexically rather than in the call).

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