[PART 2] Useful JavaScript Tips, Tricks and Best Practices

[Koyyiko]

11 – Generate a random set of alphanumeric characters

function generateRandomAlphaNum(len) {
var rdmString = "";
for( ; rdmString.length < len; rdmString += Math.random().toString(36).substr(2));
return rdmString.substr(0, len);

}

12 – Shuffle an array of numbers

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411];
numbers = numbers.sort(function(){ return Math.random() - 0.5});
/* the array numbers will be equal for example to [120, 5, 228, -215, 400, 458, -85411, 122205] */

A better option could be to implement a random sort order by code (e.g. : Fisher-Yates shuffle), than using the native sort JavaScript function. For more details take a look to this discussion.

13 – A string trim function
The classic trim function of Java, C#, PHP and many other language that remove whitespace from a string doesn’t exist in JavaScript, so we could add it to the String object.

String.prototype.trim = function(){return this.replace(/^s+|s+$/g, "");};

A native implementation of the trim() function is available in the recent JavaScript engines.

14 – Append an array to another array

var array1 = [12 , "foo" , {name "Joe"} , -2458];

var array2 = ["Doe" , 555 , 100];
Array.prototype.push.apply(array1, array2);
/* array1 will be equal to [12 , "foo" , {name "Joe"} , -2458 , "Doe" , 555 , 100] */

15 – Transform the arguments object into an array

var argArray = Array.prototype.slice.call(arguments);

16 – Verify that a given argument is a number

function isNumber{
return !isNaN(parseFloat) && isFinite;
}

17 – Verify that a given argument is an array

function isArray(obj){
return Object.prototype.toString.call(obj) === '[object Array]' ;
}

Note that if the toString() method is overridden, you will not get the expected result using this trick.

Or use…

Array.isArray(obj); // its a new Array method
You could also use instanceof if you are not working with multiple frames. However, if you have many contexts, you will get a wrong result.

var myFrame = document.createElement('iframe');
document.body.appendChild(myFrame);

var myArray = window.frames[window.frames.length-1].Array;
var arr = new myArray(a,b,10); // [a,b,10]

// instanceof will not work correctly, myArray loses his constructor
// constructor is not shared between frames
arr instanceof Array; // false

18 – Get the max or the min in an array of numbers

var numbers = [5, 458 , 120 , -215 , 228 , 400 , 122205, -85411];
var maxInNumbers = Math.max.apply(Math, numbers);
var minInNumbers = Math.min.apply(Math, numbers);

19 – Empty an array

var myArray = [12 , 222 , 1000 ];
myArray.length = 0; // myArray will be equal to [].

20 – Don’t use delete to remove an item from array
Use splice instead of using delete to delete an item from an array. Using delete replaces the item with undefined instead of the removing it from the array.

Instead of…

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ];
items.length; // return 11
delete items[3]; // return true
items.length; // return 11
/* items will be equal to [12, 548, "a", undefined × 1, 5478, "foo", 8852, undefined × 1, "Doe", 2154, 119] */

Use…

var items = [12, 548 ,'a' , 2 , 5478 , 'foo' , 8852, , 'Doe' ,2154 , 119 ];
items.length; // return 11
items.splice(3,1) ;
items.length; // return 10
/* items will be equal to [12, 548, "a", 5478, "foo", 8852, undefined × 1, "Doe", 2154, 119] */

The delete method should be used to delete an object property.