title: Even simpler way of using indexOf as a contains clause tip-number: 15 tip-username: jhogoforbroke tip-username-profile: https://twitter.com/jhogoforbroke tip-tldr: JavaScript by default does not have a contains method. And for checking existence of a substring in a string or an item in an array you may do this.
JavaScript by default does not have a contains method. And for checking existence of a substring in a string or an item in an array you may do this:
var someText = 'javascript rules';if (someText.indexOf('javascript') !== -1) {}// orif (someText.indexOf('javascript') >= 0) {}
But let’s look at these Expressjs code snippets.
for (var key in obj) { // "reserved" exports if (~['name', 'prefix', 'engine', 'before'].indexOf(key)) continue;
exports.normalizeType = function (type) { return ~type.indexOf('/') ? acceptParams(type) : { value: mime.lookup(type), params: {} };};
// key is invalidif (!~apiKeys.indexOf(key)) return next(error(401, 'invalid api key'));
The gotcha is the bitwise operator ~, “Bitwise operators perform their operations on binary representations, but they return standard JavaScript numerical values.”
It transforms -1 into 0, and 0 evaluates to false in JavaScript:
var someText = 'text';!!~someText.indexOf('tex'); // someText contains "tex" - true!~someText.indexOf('tex'); // someText NOT contains "tex" - false~someText.indexOf('asd'); // someText doesn't contain "asd" - false~someText.indexOf('ext'); // someText contains "ext" - true
ES6 introduced the includes() method and you can use it to determine whether or not a string includes another string:
'something'.includes('thing'); // true
With ECMAScript 2016 (ES7) it is even possible to use these techniques with Arrays:
!!~[1, 2, 3].indexOf(1); // true[1, 2, 3].includes(1); // true
Unfortunately, it is only supported in Chrome, Firefox, Safari 9 or above and Edge; not IE11 or lower. It’s better used in controlled environments.