On my Firefox web console, I enter the following JS
const scoreTierMins = [90, 70, 50, 30, 10, 0];
const pctScore = 75;
I want to find the index of the first element in the "scoreTierMins" array that is greater than or equal to "pctScore". So I tried this
scoreTierMins.findIndex(function(el) {el >= pctScore});
but I get the result "-1". What else am I missing? Shouldn't the result be "1" because "70" is the first element that matches the condition?
You aren't returning the result of the comparison. Though you put the expression el >= pctScore in the function body, without a return statement it's just an expression that does nothing and whose value is discarded. It's as if you wrote this function:
function compareElements(el) {
el >= pctScore;
}
When you write it out it should be clear that it's not doing anything.
Instead, return the condition like so:
const scoreTierMins = [90, 70, 50, 30, 10, 0];
const pctScore = 75;
let index = scoreTierMins.findIndex(function(el) {return el >= pctScore});
console.log(index);Or use ES6 arrow functions to be more concise: scoreTierMins.findIndex(el => el >= pctScore) - when the body of an arrow function is just an expression, it is implicitly unwrapped to el => { return el >= pctScore }.
The 'findIndex callback' should return a 'boolean'. In your case, return the condition.
I had a similar problem searching through test of Regular expression, here the Javascript (FireFox) log:
re = new RegExp("^width\\s*[:=]|^width$","gi");
/^width\s*[:=]|^width$/gi
h = ["width : 250","Height","300","top"]
Array(4) [ "width : 250", "Height", "300", "top" ]
h.findIndex(el => re.test(el))
0
h.findIndex(el => re.test(el))
-1
h.findIndex(el => re.test(el))
0
h.findIndex(el => re.test(el))
-1
If instead of "width" I search for "height" or "width" is not the first item I always get the correct answer.
I got the correct results by eliminating the g (global) flag from the regular expression because with this flag:
RegExp objects are stateful when they have the global or sticky flags set
return.scoreTierMins.findIndex(el => el >= pctScore)