👍 Add inspect function to inspect value

Author: lambdalisue

__snapshots__/inspect_test.ts.snap

@@ -0,0 +1,45 @@
+export const snapshot = {};
+
+snapshot[`inspect > string 1`] = `'"hello world"'`;
+
+snapshot[`inspect > number 1`] = `"100"`;
+
+snapshot[`inspect > bigint 1`] = `"100n"`;
+
+snapshot[`inspect > boolean 1`] = `"true"`;
+
+snapshot[`inspect > array 1`] = `"[]"`;
+
+snapshot[`inspect > array 2`] = `"[0, 1, 2]"`;
+
+snapshot[`inspect > array 3`] = `'[0, "a", true]'`;
+
+snapshot[`inspect > array 4`] = `"[0, [1, [2]]]"`;
+
+snapshot[`inspect > record 1`] = `"{}"`;
+
+snapshot[`inspect > record 2`] = `"{a: 0, b: 1, c: 2}"`;
+
+snapshot[`inspect > record 3`] = `
+'{
+  a: "a",
+  b: 1,
+  c: true
+}'
+`;
+
+snapshot[`inspect > record 4`] = `"{a: {b: {c: 0}}}"`;
+
+snapshot[`inspect > function 1`] = `"inspect"`;
+
+snapshot[`inspect > function 2`] = `"(anonymous)"`;
+
+snapshot[`inspect > null 1`] = `"null"`;
+
+snapshot[`inspect > undefined 1`] = `"undefined"`;
+
+snapshot[`inspect > symbol 1`] = `"Symbol(a)"`;
+
+snapshot[`inspect > date 1`] = `"Date"`;
+
+snapshot[`inspect > promise 1`] = `"Promise"`;

inspect.ts

@@ -0,0 +1,59 @@
+const defaultThreshold = 20;
+
+export type InspectOptions = {
+  // The maximum number of characters of a single attribute
+  threshold?: number;
+};
+
+/**
+ * Inspect a value
+ */
+export function inspect(value: unknown, options: InspectOptions = {}): string {
+  if (value === null) {
+    return "null";
+  } else if (Array.isArray(value)) {
+    return inspectArray(value, options);
+  }
+  switch (typeof value) {
+    case "string":
+      return JSON.stringify(value);
+    case "bigint":
+      return `${value}n`;
+    case "object":
+      if (value.constructor?.name !== "Object") {
+        return value.constructor?.name;
+      }
+      return inspectRecord(value as Record<PropertyKey, unknown>, options);
+    case "function":
+      return value.name || "(anonymous)";
+  }
+  return value?.toString() ?? "undefined";
+}
+
+function inspectArray(value: unknown[], options: InspectOptions): string {
+  const { threshold = defaultThreshold } = options;
+  const vs = value.map((v) => inspect(v, options));
+  const s = vs.join(", ");
+  if (s.length <= threshold) return `[${s}]`;
+  const m = vs.join(",\n");
+  return `[\n${indent(2, m)}\n]`;
+}
+
+function inspectRecord(
+  value: Record<PropertyKey, unknown>,
+  options: InspectOptions,
+): string {
+  const { threshold = defaultThreshold } = options;
+  const vs = Object.entries(value).map(([k, v]) =>
+    `${k}: ${inspect(v, options)}`
+  );
+  const s = vs.join(", ");
+  if (s.length <= threshold) return `{${s}}`;
+  const m = vs.join(",\n");
+  return `{\n${indent(2, m)}\n}`;
+}
+
+function indent(level: number, text: string): string {
+  const prefix = "  ".repeat(level);
+  return text.split("\n").map((line) => `${prefix}${line}`).join("\n");
+}

inspect_test.ts

@@ -0,0 +1,50 @@
+import {
+  assertSnapshot,
+} from "https://deno.land/[email protected]/testing/snapshot.ts";
+import { inspect } from "./inspect.ts";
+
+Deno.test("inspect", async (t) => {
+  await t.step("string", async (t) => {
+    await assertSnapshot(t, inspect("hello world"));
+  });
+  await t.step("number", async (t) => {
+    await assertSnapshot(t, inspect(100));
+  });
+  await t.step("bigint", async (t) => {
+    await assertSnapshot(t, inspect(100n));
+  });
+  await t.step("boolean", async (t) => {
+    await assertSnapshot(t, inspect(true));
+  });
+  await t.step("array", async (t) => {
+    await assertSnapshot(t, inspect([]));
+    await assertSnapshot(t, inspect([0, 1, 2]));
+    await assertSnapshot(t, inspect([0, "a", true]));
+    await assertSnapshot(t, inspect([0, [1, [2]]]));
+  });
+  await t.step("record", async (t) => {
+    await assertSnapshot(t, inspect({}));
+    await assertSnapshot(t, inspect({ a: 0, b: 1, c: 2 }));
+    await assertSnapshot(t, inspect({ a: "a", b: 1, c: true }));
+    await assertSnapshot(t, inspect({ a: { b: { c: 0 } } }));
+  });
+  await t.step("function", async (t) => {
+    await assertSnapshot(t, inspect(inspect));
+    await assertSnapshot(t, inspect(() => {}));
+  });
+  await t.step("null", async (t) => {
+    await assertSnapshot(t, inspect(null));
+  });
+  await t.step("undefined", async (t) => {
+    await assertSnapshot(t, inspect(undefined));
+  });
+  await t.step("symbol", async (t) => {
+    await assertSnapshot(t, inspect(Symbol("a")));
+  });
+  await t.step("date", async (t) => {
+    await assertSnapshot(t, inspect(new Date()));
+  });
+  await t.step("promise", async (t) => {
+    await assertSnapshot(t, inspect(new Promise(() => {})));
+  });
+});