interpolate

Replaces nested placeholders with values from an object.

Code

interpolate.ts

export type MissingInterpolationValue = "keep" | "empty" | "throw";
export type InterpolateOptions = {
  missing?: MissingInterpolationValue;
};

const readPath = (object: unknown, path: string): unknown => {
  let current = object;
  for (const segment of path.split(".")) {
    if (current === null || typeof current !== "object" || !Object.prototype.hasOwnProperty.call(current, segment)) return undefined;
    current = Reflect.get(current, segment);
  }
  return current;
};

/** Replaces {{ dot.path }} placeholders with own properties from a values object. */
export const interpolate = (
  template: string,
  values: object,
  { missing = "keep" }: InterpolateOptions = {}
): string => {
  return template.replace(/{{\s*([^{}]+?)\s*}}/g, (placeholder, path: string) => {
    const value = readPath(values, path.trim());
    if (value !== undefined && value !== null) return String(value);
    if (missing === "empty") return "";
    if (missing === "throw") throw new ReferenceError(`Missing interpolation value: ${path.trim()}`);
    return placeholder;
  });
};

Download

wget

Terminal

wget -O src/lib/interpolate.ts https://raw.githubusercontent.com/jrTilak/lazykit/HEAD/registry/functions/interpolate.ts

degit

Terminal

temp_dir="$(mktemp -d)" && bunx degit jrTilak/lazykit/registry/functions "$temp_dir" && mv "$temp_dir/interpolate.ts" src/lib/interpolate.ts && rm -r "$temp_dir"

Examples

interpolate.example.ts

import { interpolate } from "./interpolate";

const message = interpolate(
  "Hello {{ user.name }}, you have {{ count }} tasks.",
  { user: { name: "Ada" }, count: 3 }
);

Props

• template (string) — Text containing {{ dot.path }} placeholders.
• values (object) — Own properties used for replacements.
• missing — keep, empty, or throw; defaults to keep.