Using indexOf to filter an array

Question

I am trying to output the first two objects in the events array using indexOf.

This doesn't return anything:

var whiteList=['css','js'];

var events =[
    {file: 'css/style.css', type:'css'},
    {file: 'js/app.js', type:'js'},
    {file: 'index/html.html', type:'html'}
];

var fileList= events
    .filter(function(event){
    return event.type.indexOf(whiteList) >- 1 
  })

console.log(fileList);

If I change the function like this, it returns the css and js object, although I expected it to return the html object.

var fileList= events
    .filter(function(event){
    return event.type.indexOf('html') 
  })

`event.type.indexOf('html')` returns 0 (the position of the 'h') - `0` is interpreted as `false`. — J. Titus, Oct 10 '16 at 20:23

score 15 · Accepted Answer · answered Oct 10 '16 at 20:23

15

You are doing it wrong, it should go like this.

var whiteList = ['css', 'js'];

var events = [{
  file: 'css/style.css',
  type: 'css'
}, {
  file: 'js/app.js',
  type: 'js'
}, {
  file: 'index/html.html',
  type: 'html'
}];

var fileList = events.filter(function(event) {
  return whiteList.indexOf(event.type) > -1
})

console.log(fileList)

answered Oct 10 '16 at 20:23

Nenad Vracar

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2

This is perfect, and I was able to use it for another piece of code I was writing. Thanks! – Chef1075 Nov 09 '17 at 02:08

score 7 · Answer 2 · answered Oct 10 '16 at 20:39

With ES6, you could use Set for faster access with larger data sets.

var whiteList = ['css', 'js'],
    whiteSet = new Set(whiteList),
    events = [{ file: 'css/style.css', type: 'css' }, { file: 'js/app.js', type: 'js' }, { file: 'index/html.html', type: 'html' }],
    fileList = events.filter(event => whiteSet.has(event.type));

console.log(fileList);

Using indexOf to filter an array

2 Answers2

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