When is an Explicit Return Required in ES6 Arrow Functions?

In ES6, arrow functions implicitly return the expression within their concise body, eliminating the need for the return keyword in scenarios with a single expression. However, there are specific cases where an explicit return statement is still necessary.

When to Use return with Arrow Functions

• When a Block is Present: An arrow function with curly braces (a block) loses its implicit return behavior. An explicit return statement must be used to specify the function's return value. Example:

() => { console.log('Hello'); } // Implicit return, logs 'Hello'
() => { return 'Hello'; } // Explicit return, returns 'Hello'

• Ambiguous Syntax: Using braces without an explicit return can create syntactical ambiguity. For instance, the following arrow function:

(name) => {id: name}

Returns undefined because the braces indicate a block, interpreting id as a label rather than a property name.

• Multi-line Expressions: When an arrow function's expression spans multiple lines, it can be confusing to remember if return was included. To avoid errors, explicitly use return to ensure the correct return value.

Examples

Implicit Return:

(name) => name   '!'; // Implicit return, returns 'Jess!'

Explicit Return:

(name) => { return name   '!'; } // Explicit return, returns 'Jess!'

In summary, if an arrow function contains a block, has ambiguous syntax, or spans multiple lines, an explicit return statement is necessary to specify the function's return value. Otherwise, the expression in the arrow function's body is implicitly returned.