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ECMAScript is a high-level, interpreted programming language that serves as the foundation for JavaScript, JScript and ActionScript. It was first standardized by Ecma International - a non-profit standards organization - in June 1997 to ensure interoperability of web-based applications across different browsers. The standardization process involved key industry players such as Netscape and Microsoft. ECMAScript has since evolved through several editions, with ES6 (ECMAScript 2015) introducing significant changes like classes and modules. Its dynamic typing, first-class functions and prototype-based object-orientation make it an essential tool for web development today.

Ask the right questions secure the right ECMAScript talent among an increasingly shrinking pool of talent.

First 20 minutes

General ECMAScript app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in ECMAScript application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What are the different data types in ECMAScript?

The different data types in ECMAScript are Undefined, Null, Boolean, String, Symbol, BigInt, Number, and Object.

How would you declare a variable in ECMAScript?

In ECMAScript, a variable can be declared using var, let, or const keywords. For example: var x; let y; const z = 10;

Describe the difference between == and === in ECMAScript.

The == operator checks for equality of values but not type, while the === operator checks for both equality of values and type.

What is the use of 'this' keyword in ECMAScript?

'this' keyword refers to the object from where it was called. It provides a reference to the current object.

How would you create an object in ECMAScript?

An object in ECMAScript can be created using the object literal syntax, or the new keyword. For example: var obj = {}; or var obj = new Object();

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What you’re looking for early on

Does the candidate have a solid understanding of ECMAScript fundamentals?

Can the candidate solve complex problems using ECMAScript?

Is the candidate familiar with the latest ECMAScript features and updates?

Does the candidate have experience with ECMAScript testing frameworks?

Next 20 minutes

Specific ECMAScript development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What are closures in ECMAScript?

Closures are functions that have access to the parent scope, even after the parent function has closed.

Describe the difference between null and undefined in ECMAScript.

In ECMAScript, undefined means a variable has been declared but has not yet been assigned a value. Null is an assignment value that means no value or no object.

What is the use of 'use strict' in ECMAScript?

'use strict' is a directive to enforce strict mode in ECMAScript. It helps catch common coding mistakes and unsafe actions.

How would you handle exceptions in ECMAScript?

In ECMAScript, exceptions can be handled using try-catch-finally blocks. The try block contains the code that might throw an exception, the catch block handles the exception, and the finally block executes code after try and catch, regardless of the result.

What are promises in ECMAScript?

Promises in ECMAScript are objects that represent the eventual completion or failure of an asynchronous operation, and its resulting value.

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At this point, a skilled ECMAScript engineer should demonstrate strong problem-solving abilities, proficiency in ECMAScript programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with ECMAScript.

What does the following code do?
let x = 10;
let y = x++;
console.log(y);
The code declares a variable x and assigns it a value of 10. Then it declares another variable y and assigns it the value of x before incrementing x by 1. Finally, it logs the value of y to the console, which will be 10.
What will be the output of the following code?
let x = '5';
let y = +x;
console.log(typeof y);
The code first declares a variable x and assigns it a string value of '5'. It then declares another variable y and assigns it the value of x, but with a unary plus operator that converts x to a number. Finally, it logs the type of y to the console, which will be 'number'.
What does the following code do?
let arr = [1, 2, 3, 4, 5];
let sum = arr.reduce((a, b) => a + b, 0);
console.log(sum);
The code declares an array arr of numbers. It then uses the reduce method to sum up the numbers in the array, with an initial value of 0. Finally, it logs the sum to the console, which will be 15.
What does the following code do?
let promise = new Promise((resolve, reject) => {
  setTimeout(() => resolve('Done!'), 1000);
});
promise.then(alert);
The code creates a new Promise that resolves with the string 'Done!' after a delay of 1 second. It then sets up a then handler to alert the result of the Promise when it resolves.

Wrap-up questions

Final candidate for ECMAScript Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle ECMAScript application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

Describe the difference between let, const and var in ECMAScript.

var is function scoped, while let and const are block scoped. const is a read-only reference to a value, meaning the value of const can't be changed.

What are arrow functions in ECMAScript?

Arrow functions are a shorthand syntax for writing function expressions in ECMAScript. They are anonymous and change the way 'this' binds in functions.

How would you implement inheritance in ECMAScript?

In ECMAScript, inheritance can be implemented using the extends keyword in class declarations or class expressions to create a class as a child of another class.

ECMAScript application related

Product Perfect's ECMAScript development capabilities

Beyond hiring for your ECMAScript engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in ECMAScript projects, and can engage in multiple capacities.

ECMAScript Consultive assessments

ECMAScript Application Conversion Assessment ECMAScript Application Integration Assessment ECMAScript Data & Database Integration Assessment

Custom ECMAScript development projects

Custom ECMAScript App Conversion ECMAScript Custom App Development Process App UI Design for ECMAScript Facelifts

Hiring guide for ECMAScript Engineers

ECMAScript Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the ECMAScript engineer at this point.

ECMAScript Consultive assessments

Custom ECMAScript development projects