how to find index of an array element

Question

var styles = ['btx btx1', 'btx btx2', 'btx btx3', 'btx btx4'];
$('#mst').on('click', function(){
 let a = $('#btx').attr('class');
 console.log(a); // `btx btx2`
 let x = styles.findIndex(a);
 console.log(x); // error
});

error - Uncaught TypeError: btx btx2 is not a function

I'm expecting 1 as the result

• ggorlen: I think you meant indexOf rather than findIndex, which expects a function parameter, as the error tells you. VTC as typo/resolved in a way unhelpful to future visitors.
• qadenza: @ggorlen - what about this - https://www.w3schools.com/jsref/jsref_findindex.asp
• ggorlen: What about it? It says the same thing as above which is that you need to pass a function to findIndex. You could do this with styles.findIndex(e => e === a); but this is a more verbose and less efficient way to write styles.indexOf(a).

Answer 1

Use indexOf:

$('#mst').on('click', function(){
 let a = $('#btx').attr('class');
 console.log(a); // `btx btx2`
 let x = styles.indexOf(a);
 console.log(x); // error
});

• qadenza: what about this - https://www.w3schools.com/jsref/jsref_findindex.asp
• harsh_apache: see this link, explained very well: stackoverflow.com/questions/41443029/…

Answer 2

If you want to use findIndex(), the params must be function instead of a specific item.

Syntax

array.findIndex(function(currentValue, index, arr), thisValue)

var styles = ['btx btx1', 'btx btx2', 'btx btx3', 'btx btx4'];
let a = 'btx btx2';
let x = styles.findIndex(function(currentValue, index, arr){
 return currentValue === a;
});
console.log(x);

Or use indexOf()

The indexOf() method searches the array for the specified item, and returns its position.

var styles = ['btx btx1', 'btx btx2', 'btx btx3', 'btx btx4'];
let a = 'btx btx2';
let x = styles.indexOf(a);
console.log(x);

• Nguyễn Văn Phong: @qadenza Does this answer your question? Let me know if you need any help