setDefaults

SetDefaults is a common pattern or function name used to apply a baseline set of configuration values when a consumer provides only a partial configuration. The idea is to ensure that all required fields have sensible values while allowing user-supplied options to override the defaults.

In practice, setDefaults works by defining a defaults object and merging it with the user’s options. The resulting configuration contains the defaults for any missing fields and the user’s values for fields that were provided. For example, in JavaScript a typical implementation is:

function setDefaults(options) {

const defaults = { host: 'localhost', port: 3000, useSSL: false, timeout: 5000 };

return { ...defaults, ...options };

}

Here, options override defaults, and unspecified keys fall back to defaults.

Variants of this pattern include shallow versus deep merging. A shallow merge combines top-level fields, which may be insufficient for nested configuration objects. Deep merging preserves more nested defaults but can be more complex and may have performance costs. In languages that emphasize immutability, setDefaults usually returns a new object rather than mutating the input.

Common use cases include libraries, frameworks, and components that accept an options object, as well as CLI tools and services that need predictable startup configurations. Important considerations include preserving explicit falsy values (such as false or 0), validating merged results, and choosing between simple defaulting and schema-based validation. Alternatives include default parameters in function signatures or explicit configuration validation with schemas.