Always protect against potential null or undefined values before attempting property access or method calls to prevent runtime errors. This applies especially to array access, method calls like `.some()` or `.length`, and property access on objects that might be null.
Always protect against potential null or undefined values before attempting property access or method calls to prevent runtime errors. This applies especially to array access, method calls like .some() or .length, and property access on objects that might be null.
Bad practice:
// Might throw if entrypoints is undefined
if (some(entrypoints, e => project.toPath(e) === path)) { ... }
// Might throw "Cannot read property 'length' of undefined"
const length = text.length;
// Potential index out of bounds
while (sourceFile.statements[pos].end < statement.end) { ... }
// Creates keys with 'undefined' as string literal
const key = `${useOnlyExternalAliasing ? 0 : 1}|${firstRelevantLocation && getNodeId(firstRelevantLocation)}|${meaning}`;
Good practice:
// Guard with logical AND
if (entrypoints && some(entrypoints, e => project.toPath(e) === path)) { ... }
// Use optional chaining
const length = text?.length;
// Check array bounds
while (pos < sourceFile.statements.length && sourceFile.statements[pos].end < statement.end) { ... }
// Provide safe fallback value
const key = `${useOnlyExternalAliasing ? 0 : 1}|${firstRelevantLocation ? getNodeId(firstRelevantLocation) : 0}|${meaning}`;
Modern TypeScript provides several ways to handle nullable values safely: optional chaining (?.), nullish coalescing (??), and traditional guards (x !== undefined). Choose the approach that makes your code most readable while ensuring runtime safety.
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