One-line if statements in JavaScript are solid for concise conditional execution of code. They’re particularly good for simple conditions and actions that can be expressed neatly in a single line. We’ll go into more detail on all of this below.

What is the basic if statement?

Before diving into one-line if statements, you should know the basic if syntax:

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if (condition) {
  // code to be executed if condition is true
}

Use the one-line if without curly braces

For a single statement following the if condition, braces can be omitted:

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if (condition) statement;

Employ the ternary operator for if-else

The ternary operator is the true one-liner for if-else statements:

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condition ? exprIfTrue : exprIfFalse;

Combine methods or operations

Chaining methods or operations in a one-liner if statement can keep your code terse:

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if (condition) doSomething().then(doSomethingElse);

Leverage short-circuit evaluation

Short-circuiting with logical operators allows if-else constructs in one line:

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condition && actionIfTrue;
condition || actionIfFalse;

Handle assignment within one-line if

You can assign a value based on a condition in one line:

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let variable = condition ? valueIfTrue : valueIfFalse;

Use arrow functions for inline execution

Incorporate arrow functions for immediate execution within your one-liner:

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if (condition) (() => { /* code block */ })();

How to handle multiple one-line if statements

When dealing with several conditions that require one-liners, ensure they remain readable:

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if (condition1) action1;
if (condition2) action2;

Use one-liners in callbacks

One-liners can be effectively used within callback functions:

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array.forEach(element => if (condition) action);

Know when to use if vs. ternary operator

The ternary operator is concise but use a regular if when the condition or actions are too complex for a ternary to remain clear.

Consider one-liners for default values

A one-liner if can set a default value if one isn't already assigned:

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let value = existingValue || defaultValue;

Be careful with one-liners and scope

Understand the scope of variables used in one-liners to avoid reference errors:

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if (condition) let scopedVariable = 'value'; // Incorrect, `let` has block scope

Remember operator precedence

When using logical operators in one-liners, keep operator precedence in mind to avoid unexpected results:

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if (condition1 && condition2 || condition3) action;

Avoid using one-liners for function declarations

Defining functions within one-liners can lead to readability and hoisting issues:

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if (condition) function myFunc() { /* ... */ }; // Not recommended

Use one-liners with template literals

Template literals can make your one-liners more readable when dealing with strings:

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if (condition) console.log(`Action was ${actionIfTrue}`);

Understand limitations with const

Remember that const declarations cannot be used in traditional one-line if statements due to block-scoping:

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if (condition) const value = 'constant'; // SyntaxError