12 extremely useful tricks for JavaScript programmers

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In this article, TipsMake.com will share 12 extremely useful tricks for JavaScript programmers . These tips will help you reduce the amount of code as well as help the code run better. Invite you to welcome reading!

1. Convert to boolean using operator !!

Sometimes we need to check if a variable exists or has a valid value, to see them as true values . To determine, you can use !! (Double negation operator) a simple !!variable , will automatically convert any boolean data type and this variable will return false when it has values ​​like: 0 ; null ; "" ; undefined 0 ; null ; "" ; undefined 0 ; null ; "" ; undefined or NaN , otherwise it will return true . To better understand how it works, take a look at the following simple example:

 function Account(cash) { 
  this.cash = cash; 
  this.hasMoney = !!cash; 
 } 
 var account = new Account(100.50); 
 console.log(account.cash); // 100.50 
 console.log(account.hasMoney); // true 
 
 var emptyAccount = new Account(0); 
 console.log(emptyAccount.cash); // 0 
 console.log(emptyAccount.hasMoney); // false 

In the above example, if the account.cash value is greater than 0, account.hasMoney will have a value of true.

Picture 1 12 extremely useful tricks for JavaScript programmers download this picture HERE

2. Convert to number using the + operator

This procedure is excellent and easy to perform. However, it only works with numeric strings, otherwise it returns NaN (Not a Number - Not a number). Take a look at the following example:

 function toNumber(strNumber) { 
  return +strNumber; 
 } 
 console.log(toNumber("1234")); // 1234 
 console.log(toNumber("ACB")); // NaN 

This trick also works for both Date and in this case it returns the timestamp number:

 console.log(+new Date()) // 1461288164385 

3. Shorten the conditions

If you see a code like the one below:

 if (conected) { 
  login(); 
 } 

You can shorten it by combining a variable (to be validated) and a function using && (AND operator) in the middle. For example, the above code may become more concise in a line:

 conected && login(); 

You can do the same to check if the property or function exists in the object. Similar to the code below:

 user && user.login(); 

4. Set the default value using the || operator

Currently, ES6 has the default parameter feature. To simulate this feature in older browsers, you can use || (OR operator) by inserting the default value as the second parameter to use. If the first parameter returns false , the second parameter will be used as the default value. See the following example:

 function User(name, age) { 
  this.name = name || "Oliver Queen"; 
  this.age = age || 27; 
 } 
 var user1 = new User(); 
 console.log(user1.name); // Oliver Queen 
 console.log(user1.age); // 27  console.log(user1.age); // 27 var user2 = new User("Barry Allen", 25); 
 console.log(user2.name); // Barry Allen 
 console.log(user2.age); // 25 

5. Store array.length in the loop

This trick is very simple and has a great impact on performance when processing large arrays in the loop. Basically, most people use a for loop to browse the array as follows:

 for (var i = 0; i < array.length; i++) { 
  console.log(array[i]); 
 } 

It's okay to work with small arrays, but if you handle large arrays, this code will recalculate the size of the array after each iteration and that will cause a bit of delay. To avoid this, you can store the array.length in a variable to use it instead of calling array.length in each iteration:

 var length = array.length; 
 for (var i = 0; i < length; i++) { 
  console.log(array[i]); 
 } 

To make it look more compact, simply rewrite the following:

 for (var i = 0, length = array.length; i < length; i++) { 
  console.log(array[i]); 
 } 

6. Identify attributes in an object

This trick is extremely useful when you need to check if the property exists and avoid running unspecified functions or attributes. If you intend to write code that runs on multiple browsers, you can also use this technique.

For example, imagine you need to write code that is compatible with the old Web browser Internet Explorer 6 - IE6 and you want to use document.querySelector() to get some elements by their ID. However, in IE6 this function does not exist. To check if the function exists, use the in operator as the example below:

 if ('querySelector' in document) { 
  document.querySelector("#id"); 
 } else { 
  document.getElementById("id"); 
 } 

In this case, if there is no querySelector function in the document, we can use document.getElementById() instead.

7. Get the last element in the array

Array.prototype.slice(begin, end) can cut the array when you set the begin and end parameters. But if you do not enter the end parameter, this function will automatically set the maximum value for the array. Surely few people know that this function can accept negative values ​​and if you set the begin parameter to be a negative number, you will get the last element from the array:

 var array = [1, 2, 3, 4, 5, 6]; 
 console.log(array.slice(-1)); // [6] 
 console.log(array.slice(-2)); // [5,6] 
 console.log(array.slice(-3)); // [4,5,6] 

8. Short cut array

This technique can lock the array size, which is useful when you want to delete some elements of the array based on the number of elements you set. For example, if you have an array of 10 elements but you only want to get the first 5 elements, you can truncate the array, making it smaller by setting array.length = 5 . See the following example:

 var array = [1, 2, 3, 4, 5, 6]; 
 console.log(array.length); // 6 
 array.length = 3; 
 console.log(array.length); // 3 
 console.log(array); // [1,2,3] 

9. Replace the whole

The String.replace() function allows to use String and Regex to replace strings, but this function only replaces the first substring that appears. You can simulate a function replaceAll() using /g at the end of the Regex:

 var string = "john john"; 
 console.log(string.replace(/hn/, "ana")); // "joana john" 
 console.log(string.replace(/hn/g, "ana")); // "joana joana" 

10. Include the array

If you need to put two arrays together, you can use the Array.concat() function:

 var array1 = [1, 2, 3]; 
 var array2 = [4, 5, 6]; 
 console.log(array1.concat(array2)); // [1,2,3,4,5,6]; 

However, this function is not the best way to merge large arrays as it will consume a lot of memory by creating a new array. In this case, you can use Array.push.apply(arr1, arr2) instead of creating a new array, it will merge the second array into the first array thereby reducing memory usage:

 var array1 = [1, 2, 3]; 
 var array2 = [4, 5, 6]; 
 console.log(array1.push.apply(array1, array2)); // [1,2,3,4,5,6]; 

11. Convert NodeList to array

If you run document.querySelectorAll("p") , it will return an array containing DOM elements, NodeList objects. But this object doesn't have all the functions of the array like: sort() ; reduce() ; map() ; filter() sort() ; reduce() ; map() ; filter() sort() ; reduce() ; map() ; filter() . To be able to use these and many other available functions of the array, you need to convert the NodeList into an array. You only need to use the function: [].slice.call(elements) :

 var elements = document.querySelectorAll("p"); // NodeList 
 var arrayElements = [].slice.call(elements); // Now the NodeList is an array 
 var arrayElements = Array.from(elements); // This is another way of converting NodeList to Array 

12. Mix elements in the array

To tamper with the elements in the array without using separate libraries like Lodash , you only need to use the following trick:

 var list = [1, 2, 3]; 
 console.log(list.sort(function() { 
  return Math.random() - 0.5 
 })); // [2,1,3] 

Conclude

Now you have learned some useful JavaScript tricks that are mostly used to minimize code and some tricks used in popular JavaScript frameworks like Lodash, Underscore.js, Strings.js and many frameworks. other.

Hope you enjoy this article and if you still know any other useful JavaScript tips, let us know in the comment section below!

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Having fun!