javascript findIndex回调参数

Question

I'm new to javascript.

I'm trying to find the index of a specific element in an array. I read about that I can use findIndex to loop through an array. But it seems that findIndex only accept three arguments: element, index and array. What if I want change the object that is used to be compared.

For example, I want for find the index of string 'b' in array ['a','b','c'] ,

var position = ['a','b','c'].findIndex(function(element, index, array){return element==='b'})

but how do I pass 'b' as parameters that I can change to callback function

Thanks

Answer 1

What about indexOf function? You just have to pass one argument, as searched element.

 let arr = ['a','b','c']; console.log(arr.indexOf('b')); 

Answer 2

You can define the wanted character from the outside context inside the callback function:

 var wantedChar = 'c'; var position = ['a','b','c'].findIndex(function(element, index, array){return element===wantedChar}) console.log(position); 

By doing so, you can wrap all that up in a function:

 var findPos = function(arr, char){ return arr.findIndex(function(element, index, array){return element===char}); } console.log(findPos(['a','b','c'], 'c')); 

Note: as already suggested, it makes more sense to use indexOf when just comparing strings. The findIndex function in combination with a custom callback is there for more sophisticated search, eg when dealing with complex structured objects.

Answer 3

 function getPosition(){ var position = ["a","b","c"]; var a = position.indexOf("b"); document.getElementById("demo").innerHTML = a; } 

 <button onclick="getPosition()">button</button> <p id="demo"></p>