First edition

The first version of ECMAScript was released in 1997. It contains only a few basic features, like variables, functions and loops.

Editorial changes

The second version of ECMAScript is released in 1998. It contains only minor changes compared to the first version.

Added regular expressions
Added try/catch
Added switch
Added do-while

The third version of ECMAScript is released in 1999. It adds many new features, such as try/catch for error handling, new comparison operators and regular expressions.

Added "strict mode"
Added JSON support
Added String.trim()
Added Array.isArray()
Added Array iteration methods
Allows trailing commas for object literals

The fifth version of ECMAScript was released in 2009. It adds many new features, such as support for strict objects, the definition of read-only properties and the ability to define methods directly on objects.

Added let and const
Added default parameter values
Added Array.find()
Added Array.findIndex()

Classes

Spread

Template literals

Added exponential operator (**)
Added Array.includes()

Rest/spread objects

Async/wait

Added string padding
Added Object.entries()
Added Object.values()
Added async functions
Added shared memory
Allows trailing commas for function parameters

Array.find()

Array.findIndex()

Array.flat()

Array.flatMap()

The Nullish Coalescing Operator (??)

• Promise any():
  const first = await Promise.any([prom1,prom2,prom3]);
• String replaceAll()
• Numeric Separators (_)

• Method .at();
• Object.hasOwn();
• RegExp: match indices(‘d’ flag);
• Error: .cause;
• New members of Classes;
• Private Slot Checks;
• Top-level Await.