Always verify that parent objects and properties exist before accessing nested properties or calling methods on them. Use optional chaining (?.) only when the parent object might genuinely be null or undefined, not as a blanket safety measure for guaranteed values. When values can be undefined, provide meaningful defaults rather than arbitrary fallbacks.
Good examples:
// When parent might be undefined
if (navigator && navigator.userAgent) {
const isChrome = navigator.userAgent.indexOf("Chrome") >= 0
}
// When property might be undefined
const cachedTokens = chunk.usage.prompt_tokens_details?.cached_tokens || 0
// When request is guaranteed to exist
if (request.options?.canSelectMany !== undefined) { // not request?.options
Avoid:
// Unnecessary optional chaining on guaranteed values
request?.options?.canSelectMany // when request is never null
// Accessing without null checks
const isChrome = navigator.userAgent.indexOf("Chrome") >= 0 // navigator might be undefined
// Arbitrary defaults that cause calculation errors
let effectiveOutputPrice = modelInfo.outputPrice || 0 // should use meaningful default
This prevents runtime errors from null reference exceptions and ensures more predictable behavior when handling optional data.
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