ShaharAmir
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JavaScript2 min read

Nullish Coalescing vs OR Operator

Why ?? is better than || for default values

S
Shahar Amir

Nullish Coalescing vs OR Operator

You've probably used || for default values:

javascript
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const name = user.name || "Anonymous";

But there's a problem.

The || Problem

The OR operator treats these as falsy:

  • null
  • undefined
  • 0
  • "" (empty string)
  • false

javascript
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const count = 0;
const result = count || 10;
// result is 10, not 0! 😱

Sometimes 0 or "" are valid values you want to keep.

Enter Nullish Coalescing (??)

The ?? operator only falls back for null or undefined:

javascript
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const count = 0;
const result = count ?? 10;
// result is 0 ✅


const name = "";
const displayName = name ?? "Anonymous";
// displayName is "" ✅

Comparison

javascript
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// Using ||
false || "default"    // "default"
0 || "default"        // "default"
"" || "default"       // "default"
null || "default"     // "default"
undefined || "default" // "default"


// Using ??
false ?? "default"    // false
0 ?? "default"        // 0
"" ?? "default"       // ""
null ?? "default"     // "default"
undefined ?? "default" // "default"

Real-World Examples

javascript
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// API response with optional fields
const timeout = config.timeout ?? 5000;
const retries = options.retries ?? 3;


// Form values
const quantity = input.value ?? 1;


// Feature flags
const isEnabled = settings.feature ?? false;

When to Use Which

Use ?? when:

  • 0, "", or false are valid values
  • Working with optional config/settings
  • Parsing user input

Use || when:

  • You want to replace ALL falsy values
  • Building boolean conditions

Default to ?? for most cases. It's what you usually mean.

#operators#es2020#fundamentals

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