index.js #1

'use strict';
module.exports = function (arr, predicate, ctx) {
	if (typeof Array.prototype.findIndex === 'function') {
		return arr.findIndex(predicate, ctx);
	}

	if (typeof predicate !== 'function') {
		throw new TypeError('predicate must be a function');
	}

	var list = Object(arr);
	var len = list.length;

	if (len === 0) {
		return -1;
	}

	for (var i = 0; i < len; i++) {
		if (predicate.call(ctx, list[i], i, list)) {
			return i;
		}
	}

	return -1;
};