ds-algo-study

<h2 id="clone-an-object">Clone an object</h2> pre data-role="codeBlock" data-info="js" class="language-javascript"><code> clone(x)</code></pre> Can clone any primitive type, array, and object. If x has a function clone, this function will be invoked to clone the object. >param {} x >return {} clone <div id=">pre data-role=" codeBlock" data-info="js" class="language-javascript"><code><a title="1"></a> <a id=-2" title="2"></a> <a id=-3" title="3">export function clone(x) {</a> <a id=-4" title="4"> const type = typeof x;</a> <a id=-5" title="5"> // immutable primitive types</a> <a id=-6" title="6"> if (</a> <a id=-7" title="7"> type === "number" ||</a> <a id=-8" title="8"> type === "string" ||</a> <a id=-9" title="9"> type === "boolean" ||</a> <a id=-10" title="10"> x === null ||</a> <a id=-11" title="11"> x === undefined</a> <a id=-12" title="12"> ) {</a> <a id=-13" title="13"> return x;</a> <a id=-14" title="14"> }</a> <a id=-15" title="15"> // use clone function of the object when available</a> <a id=-16" title="16"> if (typeof x.clone === "function") {</a> <a id=-17" title="17"> return x.clone();</a> <a id=-18" title="18"> }</a> <a id=-19" title="19"> // array</a> <a id=-20" title="20"> if (Array.isArray(x)) {</a> <a id=-21" title="21"> return x.map(function (value) {</a> <a id=-22" title="22"> return clone(value);</a> <a id=-23" title="23"> });</a> <a id=-24" title="24"> }</a> <a id=-25" title="25"> if (x instanceof Date) return new Date(x.valueOf());</a> <a id=-26" title="26"></a> <a id=-27" title="27"> // object</a> <a id=-28" title="28"> return mapObject(x, clone);</a> <a id=-29" title="29">}</a></code></pre></div> <h2 id="apply-map-to-all-properties-of-an-object">Apply map to all properties of an object</h2> <blockquote> param {Object} object param {function} callback return {Object} Returns a copy of the object with mapped properties </blockquote> <div id=">pre data-role=" codeBlock" data-info="js" class="language-javascript"><code><a title="1"></a> <a title="2"></a> <a title="3">export function mapObject(object, callback) {</a> <a id=-4" title="4"> const clone = {};</a> <a id=-5" title="5"> for (const key in object) {</a> <a id=-6" title="6"> if (hasOwnProperty(object, key)) {</a> <a id=-7" title="7"> clone[key] = callback(object[key]);</a> <a id=-8" title="8"> }</a> <a id=-9" title="9"> }</a> <a id=-10" title="10"> return clone;</a> <a id=-11" title="11">}</a></code></pre></div> <h2 id="extend-object-a-with-the-properties-of-object-b">Extend object a with the properties of object b</h2> <blockquote> param {Object} a param {Object} b return {Object} a </blockquote> <div id=">pre data-role=" codeBlock" data-info="js" class="language-javascript"><code><a title="1"></a> <a id=-2" title="2"></a> <a id=-3" title="3">export function extend(a, b) {</a> <a id=-4" title="4"> for (const prop in b) {</a> <a id=-5" title="5"> if (hasOwnProperty(b, prop)) {</a> <a id=-6" title="6"> a[prop] = b[prop];</a> <a id=-7" title="7"> }</a> <a id=-8" title="8"> }</a> <a id=-9" title="9"> return a;</a> <a id=-10" title="10">}</a></code></pre></div> <h2 id="deep-test-equality-of-all-fields-in-two-pairs-of-arrays-or-objects.">Deep test equality of all fields in two pairs of arrays or objects.</h2> Compares values and functions strictly (ie. 2 is not the same as ‘2'). >param {Array | Object} a >param {Array | Object} b >returns {boolean} <div> <pre data-role="codeBlock" data-info="js" class="language-javascript"> ><code><a title="1"></a> <a id=-2" title="2"></a> <a id=-3" title="3">export function deepStrictEqual(a, b) {</a> <a id=-4" title="4"> let prop, i, len;</a> <a id=-5" title="5"> if (Array.isArray(a)) {</a> <a id=-6" title="6"> if (!Array.isArray(b)) {</a> <a id=-7" title="7"> return false;</a> <a id=-8" title="8"> }</a> <a id=-9" title="9"> if (a.length !== b.length) {</a> <a id=-10" title="10"> return false;</a> <a id=-11" title="11"> }</a> <a id=-12" title="12"> for (i = 0, len = a.length; i < len; i++) {</a> <a id=-13" title="13"> if (!deepStrictEqual(a[i], b[i])) {</a> <a id=-14" title="14"> return false;</a> <a id=-15" title="15"> }</a> <a id=-16" title="16"> }</a> <a id=-17" title="17"> return true;</a> <a id=-18" title="18"> } else if (typeof a === "function") {</a> <a id=-19" title="19"> return a === b;</a> <a id=-20" title="20"> } else if (a instanceof Object) {</a> <a id=-21" title="21"> if (Array.isArray(b) || !(b instanceof Object)) {</a> <a id=-22" title="22"> return false;</a> <a id=-23" title="23"> }</a> <a id=-24" title="24"> for (prop in a) {</a> <a id=-25" title="25"> // noinspection JSUnfilteredForInLoop</a> <a id=-26" title="26"> if (!(prop in b) || !deepStrictEqual(a[prop], b[prop])) {</a> <a id=-27" title="27"> return false;</a> <a id=-28" title="28"> }</a> <a id=-29" title="29"> }</a> <a id=-30" title="30"> for (prop in b) {</a> <a id=-31" title="31"> // noinspection JSUnfilteredForInLoop</a> <a id=-32" title="32"> if (!(prop in a) || !deepStrictEqual(a[prop], b[prop])) {</a> <a id=-33" title="33"> return false;</a> <a id=-34" title="34"> }</a> <a id=-35" title="35"> }</a> <a id=-36" title="36"> return true;</a> <a id=-37" title="37"> } else {</a> <a id=-38" title="38"> return a === b;</a> <a id=-39" title="39"> }</a> <a id=-40" title="40">}</a></code></pre></div> <h2 id="recursively-flatten-a-nested-object.">Recursively flatten a nested object.</h2> <blockquote> param {Object} nestedObject return {Object} Returns the flattened object </blockquote> <div id=">pre data-role=" codeBlock" data-info="js" class="language-javascript"><code><a title="1"></a> <a id=-2" title="2"></a> <a id=-3" title="3">export function deepFlatten(nestedObject) {</a> <a id=-4" title="4"> const flattenedObject = {};</a> <a id=-5" title="5"> _deepFlatten(nestedObject, flattenedObject);</a> <a id=-6" title="6"> return flattenedObject;</a> <a id=-7" title="7">}</a> <a id=-8" title="8">// helper function used by deepFlatten</a> <a id=-9" title="9">function _deepFlatten(nestedObject, flattenedObject) {</a> <a id=-10" title="10"> for (const prop in nestedObject) {</a> <a id=-11" title="11"> if (hasOwnProperty(nestedObject, prop)) {</a> <a id=-12" title="12"> const value = nestedObject[prop];</a> <a id=-13" title="13"> if (typeof value === "object" && value !== null) {</a> <a id=-14" title="14"> _deepFlatten(value, flattenedObject);</a> <a id=-15" title="15"> } else {</a> <a id=-16" title="16"> flattenedObject[prop] = value;</a> <a id=-17" title="17"> }</a> <a id=-18" title="18"> }</a> <a id=-19" title="19"> }</a> <a id=-20" title="20">}</a></code></pre></div> <h2 id="test-whether-the-current-javascript-engine-supports-object.defineproperty">Test whether the current JavaScript engine supports Object.defineProperty</h2> <blockquote> returns {boolean} returns true if supported </blockquote> <div id="cb7"> <pre data-role="codeBlock" data-info="js" class="language-javascript"> ><code><a title="1"></a> <a id="cb7-2" title="2"></a> <a id="cb7-3" title="3">export function canDefineProperty() {</a> <a id="cb7-4" title="4"> // test needed for broken IE8 implementation</a> <a id="cb7-5" title="5"> try {</a> <a id="cb7-6" title="6"> if (Object.defineProperty) {</a> <a id="cb7-7" title="7"> Object.defineProperty({}, "x", { get: function () {} });</a> <a id="cb7-8" title="8"> return true;</a> <a id="cb7-9" title="9"> }</a> <a id="cb7-10" title="10"> } catch (e) {}</a> <a id="cb7-11" title="11"> return false;</a> <a id="cb7-12" title="12">}</a></code></pre></div> <h2 id="attach-a-lazy-loading-property-to-a-constant.">Attach a lazy loading property to a constant.</h2> The given function <code>fn</code> is called once when the property is first requested. >param {Object} object Object where to add the property >param {string} prop Property name >param {Function} valueResolver Function returning the property value. Called without arguments. <div id="cb8"> <pre data-role="codeBlock" data-info="js" class="language-javascript"> ><code><a title="1"></a> <a id="cb8-2" title="2"></a> <a id="cb8-3" title="3">export function lazy(object, prop, valueResolver) {</a> <a id="cb8-4" title="4"> let _uninitialized = true;</a> <a id="cb8-5" title="5"> let _value;</a> <a id="cb8-6" title="6"> Object.defineProperty(object, prop, {</a> <a id="cb8-7" title="7"> get: function () {</a> <a id="cb8-8" title="8"> if (_uninitialized) {</a> <a id="cb8-9" title="9"> _value = valueResolver();</a> <a id="cb8-10" title="10"> _uninitialized = false;</a> <a id="cb8-11" title="11"> }</a> <a id="cb8-12" title="12"> return _value;</a> <a id="cb8-13" title="13"> },</a> <a id="cb8-14" title="14"> set: function (value) {</a> <a id="cb8-15" title="15"> _value = value;</a> <a id="cb8-16" title="16"> _uninitialized = false;</a> <a id="cb8-17" title="17"> },</a> <a id="cb8-18" title="18"> configurable: true,</a> <a id="cb8-19" title="19"> enumerable: true,</a> <a id="cb8-20" title="20"> });</a> <a id="cb8-21" title="21">}</a></code></pre></div> <h2 id="get-a-nested-property-from-an-object">Get a nested property from an object</h2> <blockquote> param {Object} object param {string | string[]} path returns {Object} </blockquote> <div id="cb9"> <pre data-role="codeBlock" data-info="js" class="language-javascript"> ><code><a title="1"></a> <a id="cb9-2" title="2"></a> <a id="cb9-3" title="3">export function get(object, path) {</a> <a id="cb9-4" title="4"> if (typeof path === "string") {</a> <a id="cb9-5" title="5"> if (isPath(path)) {</a> <a id="cb9-6" title="6"> return get(object, path.split("."));</a> <a id="cb9-7" title="7"> } else {</a> <a id="cb9-8" title="8"> return object[path];</a> <a id="cb9-9" title="9"> }</a> <a id="cb9-10" title="10"> }</a> <a id="cb9-11" title="11"> let child = object;</a> <a id="cb9-12" title="12"> for (let i = 0; i < path.length; i++) {</a> <a id="cb9-13" title="13"> const key = path[i];</a> <a id="cb9-14" title="14"> child = child ? child[key] : undefined;</a> <a id="cb9-15" title="15"> }</a> <a id="cb9-16" title="16"> return child;</a> <a id="cb9-17" title="17">}</a></code></pre></div> <h2 id="set-a-nested-property-in-an-object">Set a nested property in an object</h2> Mutates the object itself If the path doesn't exist, it will be created >param {Object} object >param {string | string[]} path >param {} value >returns {Object} <div id=0"> <pre data-role="codeBlock" data-info="js" class="language-javascript"> ><code><a id=0-1" title="1"></a> <a id=0-2" title="2"></a> <a id=0-3" title="3">export function set(object, path, value) {</a> <a id=0-4" title="4"> if (typeof path === "string") {</a> <a id=0-5" title="5"> if (isPath(path)) {</a> <a id=0-6" title="6"> return set(object, path.split("."), value);</a> <a id=0-7" title="7"> } else {</a> <a id=0-8" title="8"> object[path] = value;</a> <a id=0-9" title="9"> return object;</a> <a id=0-10" title="10"> }</a> <a id=0-11" title="11"> }</a> <a id=0-12" title="12"> let child = object;</a> <a id=0-13" title="13"> for (let i = 0; i < path.length - 1; i++) {</a> <a id=0-14" title="14"> const key = path[i];</a> <a id=0-15" title="15"> if (child[key] === undefined) {</a> <a id=0-16" title="16"> child[key] = {};</a> <a id=0-17" title="17"> }</a> <a id=0-18" title="18"> child = child[key];</a> <a id=0-19" title="19"> }</a> <a id=0-20" title="20"> if (path.length > 0) {</a> <a id=0-21" title="21"> const lastKey = path[path.length - 1];</a> <a id=0-22" title="22"> child[lastKey] = value;</a> <a id=0-23" title="23"> }</a> <a id=0-24" title="24"> return object;</a> <a id=0-25" title="25">}</a></code></pre></div>