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1. How do I hide all specified elements?

const hide = (... el) => [...el].forEach(e => (e.style.display = "none")); // Example hide(document.querySelectorAll("img")); // Hide all <img /> elements on the pageCopy the code

2. How do I check if an element has a specified class?

const hasClass = (el, className) => el.classList.contains(className); 

// Example 
hasClass(document.querySelector("p.special"), "special"); // true
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3. How to switch the class of an element?

const toggleClass = (el, className) => el.classList.toggle(className); // Example toggleClass(document.querySelector( p.special ), special ); // This paragraph no longer has the "special" classCopy the code

4, how to get the current page scroll position?

const getScrollPosition = (el = window) => ({ x: el.pageXOffset ! == undefined ? el.pageXOffset : el.scrollLeft, y: el.pageYOffset ! == undefined ? el.pageYOffset : el.scrollTop }); // Example getScrollPosition(); // {x: 0, y: 200}Copy the code

5. How to evaluate scrolling to the top of the page?

const scrollToTop = () => { const c = document.documentElement.scrollTop || document.body.scrollTop; if (c > 0) { window.requestAnimationFrame(scrollToTop); window.scrollTo(0, c - c / 8); }}; // Example scrollToTop();Copy the code

How do I check if a parent element contains children

const elementContains = (parent, child) => parent ! == child && parent.contains(child); // Examples elementContains(document.querySelector("head"), document.querySelector("title")); // true elementContains(document.querySelector("body"), document.querySelector("body")); // falseCopy the code

7. How do I check if the specified element is visible in the viewport?

const elementIsVisibleInViewport = (el, partiallyVisible = false) => { const { top, left, bottom, right } = el.getBoundingClientRect(); const { innerHeight, innerWidth } = window; return partiallyVisible ? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) && ((left > 0 && left < innerWidth) || (right >  0 && right < innerWidth)) : top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth; }; // Examples elementIsVisibleInViewport(el); / / (not visible) completely elementIsVisibleInViewport (el, true); // (partially visible)Copy the code

8. How do I get all the images in an element?

const getImages = (el, includeDuplicates = false) => { const images = [...el.getElementsByTagName("img")].map(img => img.getAttribute("hide"));  return includeDuplicates ? images : [...new Set(images)]; }; // Examples getImages(document, true); // ["image1.jpg", "image2.png", "image1.png", "..."]  getImages(document, false); // ["image1.jpg", "image2.png", "..."]Copy the code

9. How to tell whether the device is mobile or desktop?

const detectDeviceType = () => /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) ? "Mobile" : "Desktop"; 

// Example 
detectDeviceType(); // "Mobile" or "Desktop"
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How do I get the current URL?

const currentURL = () => window.location.href; 

// Example 
currentURL(); // "https://google.com"
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11, how to create an object containing the current URL parameters?

const getURLParameters = url => (url.match(/([^?=&]+)(=([^&]*))/g) || []).reduce((a, v) => ((a[v.slice(0, v.indexOf( = ))] = v.slice(v.indexOf( = ) + 1)), a), {}); // Examples getURLParameters("http://url.com/page?n=Adam&s; =Smith"); // {n: "Adam", s: "Smith"} getURLParameters("google.com"); / / {}Copy the code

12. How do YOU encode a set of form elements as an object?

const formToObject = form => Array.from(new FormData(form)).reduce((acc, [key, value]) => ({ ... acc, [key]: value }),{}); // Example formToObject(document.querySelector("#form")); // { email: "[email protected]", name: "Test Name" }Copy the code

How do I retrieve a set of properties indicated by a given selector from an object?

const get = (from, ... selectors) => [...selectors].map(s => s.replace(/[([^[]]*)]/g, ".$1.").split(".").filter(t => t ! == "").reduce((prev, cur) => prev && prev[cur], from)); const obj = { selector: { to: { val: "val to select" } }, target: [1, 2, { a: "test" }] }; // Example get(obj, "selector.to.val", "target[0]", "target[2].a"); // ["val to select", 1, "test"]Copy the code

14. How to call the provided function after waiting a certain amount of time (in milliseconds)?

const delay = (fn, wait, ... args) => setTimeout(fn, wait, ... args); delay(function(text) { console.log(text); }, 1000, "later"); // Record "later" after one secondCopy the code

15. How do I trigger a specific event on a given element and optionally pass custom data?

const triggerEvent = (el, eventType, detail) => el.dispatchEvent(new CustomEvent(eventType, { detail })); 

// Examples 
triggerEvent(document.getElementById("myId"), "click"); 
triggerEvent(document.getElementById( myId ), "click", { username: "bob" });
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How do I remove an element’s event listener?

const off = (el, evt, fn, opts = false) => el.removeEventListener(evt, fn, opts); const fn = () => console.log("!" ); document.body.addEventListener("click", fn); off(document.body, "click", fn); // no longer logs "!" upon clicking on the pageCopy the code

How do I get a readable format for a given number of milliseconds?

const formatDuration = ms => { if (ms < 0) ms = -ms; const time = { day: Math.floor(ms / 86400000), hour: Math.floor(ms / 3600000) % 24, minute: Math.floor(ms / 60000) % 60, second: Math.floor(ms / 1000) % 60, millisecond: Math.floor(ms) % 1000 }; return Object.entries(time).filter(val => val[1] ! == 0).map(([key, val]) => `${val} ${key}${val ! = = 1? "s" : ""}`).join(","); }; // Examples formatDuration(1001); // 1 second, 1 millisecond formatDuration(34325055574); // 397 days, 6 hours, 44 minutes, 15 seconds, 574 millisecondsCopy the code

How do I get the number of days between two dates?

const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24); // Example getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")); / / 9Copy the code

19, How to GET the passed URL

const httpGet = (url, callback, err = console.error) => {     
    const request = new XMLHttpRequest();     
    request.open("GET", url, true);
    request.onload = () => callback(request.responseText);     
    request.onerror = () => err(request);     
    request.send(); 
}; 

httpGet(
    "https://jsonplaceholder.typicode.com/posts/1", 
    console.log
); 
// Logs: {"userId": 1, "id": 1, "title": "sample title", "body": "my text"}
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20, How to make a POST request to the passed URL?

const httpPost = (url, data, callback, err = console.error) => {     
    const request = new XMLHttpRequest();     
    request.open( POST , url, true);     
    request.setRequestHeader( Content-type ,  application/json; charset=utf-8 );     
    request.onload = () => callback(request.responseText);     
    request.onerror = () => err(request);     
    request.send(data); 
}; 
const newPost = { 
    userId: 1, 
    id: 1337, 
    title:  Foo ,     
    body:  bar bar bar  
}; 

const data = JSON.stringify(newPost); 
httpPost(
    "https://jsonplaceholder.typicode.com/posts", 
    data,
    console.log
); 
// Logs: {"userId": 1, "id": 1337, "title": "Foo", "body": "bar bar bar"}
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How do I create a timer with a specified range, step, and duration for a specified selector?

const counter = (selector, start, end, step = 1, duration = 2000) => { let current = start, _step = (end - start) * step < 0 ? -step : step, timer = setInterval(() => { current += _step; document.querySelector(selector).innerHTML = current; if (current >= end) document.querySelector(selector).innerHTML = end; if (current >= end) clearInterval(timer); }, Math.abs(Math.floor(duration / (end - start)))); return timer; }; // Example counter( #my-id , 1, 1000, 5, 2000); // Create a two-second timer for the element with id="my-id"Copy the code

How do I copy a string to the clipboard?

const copyToClipboard = str => { const el = document.createElement( textarea ); el.value = str; el.setAttribute( readonly , ); el.style.position = absolute ; el.style.left = -9999px ; document.body.appendChild(el); const selected = document.getSelection().rangeCount > 0 ? document.getSelection().getRangeAt(0) : false; el.select(); document.execCommand( copy ); document.body.removeChild(el); if (selected) { document.getSelection().removeAllRanges(); document.getSelection().addRange(selected); }}; // Example copyToClipboard( Lorem ipsum ); // Lorem ipsum copied to clipboard.Copy the code

23. How do I determine if a page’s browser TAB is foreground active?

const isBrowserTabFocused = () => ! document.hidden; // Example isBrowserTabFocused(); // trueCopy the code

24, If a directory does not exist, how to create it?

const fs = require( fs ); const createDirIfNotExists = dir => (! fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined); // Example createDirIfNotExists( test ); // creates the directory test , if it doesn t existCopy the code