util: add inspect.defaultOptions

Adds util.inspect.defaultOptions which allows customization of the
default util.inspect options, which is useful for functions like
console.log or util.format which implicitly call into util.inspect.

PR-URL: #8013
Fixes: #7566
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>

doc/api/util.md

@@ -271,6 +271,23 @@ util.inspect(obj);
   // "{ bar: 'baz' }"
 ```
 
+### util.inspect.defaultOptions
+
+The `defaultOptions` value allows customization of the default options used by
+`util.inspect`. This is useful for functions like `console.log` or
+`util.format` which implicitly call into `util.inspect`. It shall be set to an
+object containing one or more valid [`util.inspect()`][] options. Setting
+option properties directly is also supported.
+
+```js
+const util = require('util');
+const arr = Array(101);
+
+console.log(arr); // logs the truncated array
+util.inspect.defaultOptions.maxArrayLength = null;
+console.log(arr); // logs the full array
+```
+
 ## Deprecated APIs
 
 The following APIs have been deprecated and should no longer be used. Existing
@@ -662,6 +679,7 @@ similar built-in functionality through [`Object.assign()`].
 [`Array.isArray`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray
 [constructor]: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Object/constructor
 [semantically incompatible]: https://github.com/nodejs/node/issues/4179
+[`util.inspect()`]: #util_util_inspect_object_options
 [Customizing `util.inspect` colors]: #util_customizing_util_inspect_colors
 [`Error`]: errors.html#errors_class_error
 [`console.log()`]: console.html#console_console_log_data

lib/util.js

@@ -6,7 +6,16 @@ const internalUtil = require('internal/util');
 const binding = process.binding('util');
 
 const isError = internalUtil.isError;
-const kDefaultMaxLength = 100;
+
+const inspectDefaultOptions = Object.seal({
+  showHidden: false,
+  depth: 2,
+  colors: false,
+  customInspect: true,
+  showProxy: false,
+  maxArrayLength: 100,
+  breakLength: 60
+});
 
 var Debug;
 var simdFormatters;
@@ -176,29 +185,31 @@ function inspect(obj, opts) {
     stylize: stylizeNoColor
   };
   // legacy...
-  if (arguments.length >= 3) ctx.depth = arguments[2];
-  if (arguments.length >= 4) ctx.colors = arguments[3];
+  if (arguments[2] !== undefined) ctx.depth = arguments[2];
+  if (arguments[3] !== undefined) ctx.colors = arguments[3];
   if (typeof opts === 'boolean') {
     // legacy...
     ctx.showHidden = opts;
-  } else if (opts) {
-    // got an "options" object
-    exports._extend(ctx, opts);
   }
-  // set default options
-  if (ctx.showHidden === undefined) ctx.showHidden = false;
-  if (ctx.depth === undefined) ctx.depth = 2;
-  if (ctx.colors === undefined) ctx.colors = false;
-  if (ctx.customInspect === undefined) ctx.customInspect = true;
-  if (ctx.showProxy === undefined) ctx.showProxy = false;
+  // Set default and user-specified options
+  ctx = Object.assign({}, inspect.defaultOptions, ctx, opts);
   if (ctx.colors) ctx.stylize = stylizeWithColor;
-  if (ctx.maxArrayLength === undefined) ctx.maxArrayLength = kDefaultMaxLength;
   if (ctx.maxArrayLength === null) ctx.maxArrayLength = Infinity;
-  if (ctx.breakLength === undefined) ctx.breakLength = 60;
   return formatValue(ctx, obj, ctx.depth);
 }
-exports.inspect = inspect;
 
+Object.defineProperty(inspect, 'defaultOptions', {
+  get: function() {
+    return inspectDefaultOptions;
+  },
+  set: function(options) {
+    if (options === null || typeof options !== 'object') {
+      throw new TypeError('"options" must be an object');
+    }
+    Object.assign(inspectDefaultOptions, options);
+    return inspectDefaultOptions;
+  }
+});
 
 // http://en.wikipedia.org/wiki/ANSI_escape_code#graphics
 inspect.colors = {
@@ -231,6 +242,7 @@ inspect.styles = {
   'regexp': 'red'
 };
 
+exports.inspect = inspect;
 
 function stylizeWithColor(str, styleType) {
   var style = inspect.styles[styleType];

test/parallel/test-util-inspect.js

@@ -43,6 +43,13 @@ assert.equal(util.inspect(Object.create({},
   '{ visible: 1 }'
 );
 
+assert(/Object/.test(
+  util.inspect({a: {a: {a: {a: {}}}}}, undefined, undefined, true)
+));
+assert(!/Object/.test(
+  util.inspect({a: {a: {a: {a: {}}}}}, undefined, null, true)
+));
+
 for (const showHidden of [true, false]) {
   const ab = new ArrayBuffer(4);
   const dv = new DataView(ab, 1, 2);
@@ -723,3 +730,37 @@ checkAlignment(new Map(big_array.map(function(y) { return [y, null]; })));
   assert.strictEqual(oneLine, util.inspect(obj, {breakLength: breakpoint + 1}));
   assert.strictEqual(twoLines, '{ foo: \'abc\',\n  bar: \'xyz\' }');
 }
+
+// util.inspect.defaultOptions tests
+{
+  const arr = Array(101);
+  const obj = {a: {a: {a: {a: 1}}}};
+
+  const oldOptions = Object.assign({}, util.inspect.defaultOptions);
+
+  // Set single option through property assignment
+  util.inspect.defaultOptions.maxArrayLength = null;
+  assert(!/1 more item/.test(util.inspect(arr)));
+  util.inspect.defaultOptions.maxArrayLength = oldOptions.maxArrayLength;
+  assert(/1 more item/.test(util.inspect(arr)));
+  util.inspect.defaultOptions.depth = null;
+  assert(!/Object/.test(util.inspect(obj)));
+  util.inspect.defaultOptions.depth = oldOptions.depth;
+  assert(/Object/.test(util.inspect(obj)));
+  assert.strictEqual(
+    JSON.stringify(util.inspect.defaultOptions),
+    JSON.stringify(oldOptions)
+  );
+
+  // Set multiple options through object assignment
+  util.inspect.defaultOptions = {maxArrayLength: null, depth: null};
+  assert(!/1 more item/.test(util.inspect(arr)));
+  assert(!/Object/.test(util.inspect(obj)));
+  util.inspect.defaultOptions = oldOptions;
+  assert(/1 more item/.test(util.inspect(arr)));
+  assert(/Object/.test(util.inspect(obj)));
+  assert.strictEqual(
+    JSON.stringify(util.inspect.defaultOptions),
+    JSON.stringify(oldOptions)
+  );
+}