Array.prototype.findIndex makes finding items in arrays easier
takes a compare function, returns the index where it returned true
const foundAt = [false, true].findIndex(item);
assert.equal(foundAt, 1);
returns the first position it was found at
const foundAt = [0, 1, 1, 1].findIndex(item => item = 1);
assert.equal(foundAt, 1);
returns -1 when nothing was found
const foundAt = [1, 2, 3].findIndex(item => item > 1);
assert.equal(foundAt, -1);
the findIndex callback gets the item, index and array as arguments
const three = 3;
const containsThree = arr => arr.indexOf(three) > -1;
function theSecondThree(index, arr) {
const preceedingItems = arr.slice(0, index);
return containsThree(preceedingItems);
}
const foundAt = [1, 1, 2, 3, 3, 3].findIndex(theSecondThree);
assert.equal(foundAt, 4);
combined with destructuring complex compares become short
const bob = {name: 'Bob'};
const alice = {name: 'Alice'};
const foundAt = [bob, alice].findIndex(({name:{length:l}}) => length > 3);
assert.equal(foundAt, 1);