What are Short Circuits?

Short-circuiting, also often called a short circuit evaluation uses logical operations to return early. They are often used as short if statements or setting default values. For example:

const fileName = this.fileName || '😶';

The example above uses the logical OR operator. If this.fileName is undefined, it will fall back to the provided values after the operator. This is equivalent to an if-else statement:

let fileName;

if (this.fileName) {
    fileName = this.fileName;
} else {
    fileName = '😶';
}

// or
let fileName = this.fileName;

if (!this.fileName) {
    fileName = '😶';
}

Similarily, you can use logical AND to set a value to true or false, only if all operands are the same:

hasFireworks && makeItFestive();

This will only execute the function if hasFireworks is true. It is equivalent to the following if statement:

if (hasFireworks) {
  makeItFestive();
}

A common use case is to return a true or false value, based on multiple conditions:

// Returns true, if all values are evaluated to true
// Returns false, if all values are evaluated to false
return value > this.min && value < this.max;

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Resources:

• The Logical OR operator
• The Logical AND operator