easy== vs equals
What is the result?
let arr = ["a", "b", "c"];
arr.reverse();
console.log(arr);JavaScript Fundamentals
Closures, scope, equality: the bread and butter every JS dev needs.
- Questions
- 10
- Tier
- Starter
- Language
- JavaScript
- Time
- ~12 min
Difficulty mix: 6 easy, 3 medium and 1 hard. The questions are drawn from the JavaScript library at the moment you start, so sitting the test twice does not give you the same paper.
What this test can pull from
42 JavaScript topics are in scope. These are the real topic labels on the questions.
- array map filter reduce
- primitives and typeof
- ToPrimitive coercion algorithm
- let const var and scope
- template literals
- Promise.all race allSettled
- object destructuring
- prototype chain internals
- this in callbacks vs methods
- structuredClone
- this-binding spec edge cases
- property descriptors
- Map Set WeakMap
- Symbol registry
- immutability patterns
- getters and setters
- SharedArrayBuffer and Atomics
- microtask vs macrotask ordering
- generators and yield
- typed arrays and ArrayBuffer
- Proxy and Reflect
- generator return throw protocol
- closures as a pattern
- ES module resolution algorithm
- custom iterables Symbol.iterator
- hidden classes and inline caches
- Error subclassing
- == vs equals
- closures and memory retention
- recursion and stack limits
Questions of the kind this test asks
Six real JavaScript questions from the same pool, snippet included. The answer options and explanations are not shown here. Those come after you attempt them.
easyarray map filter reduce
What will this print?
let arr = ["a", "b"];
arr.push("c");
console.log(arr);easyprimitives and typeof
What does the following code return?
typeof null === "object"easyarray map filter reduce
What is the output?
let arr = [[1, 2], [3, 4, 5]];
console.log(arr.flat());easythis in callbacks vs methods
What will this code output?
const obj = {
name: "Hello",
sayHello: function() {
console.log(this.name);
}
};
obj.sayHello();easytemplate literals
What is the output?
let str = "Hello World";
console.log(str.toUpperCase());Prefer to pick your own questions? Browse all JavaScript questions. See the other 10 tests.