In this post, I will cover some things that are cool and most of you're unaware of. Let' see them.
Null is an Object
Null is an object. Despite this, null is not considered as an instance of an object. This brings us back to sanity, because if null is the absence of value, then it obviously can't be an instance of anything. Hence, the following evaluates to false:
alert(typeof null); // alerts 'object'
alert(null instanceof Object); // evaluates false
NaN is a Number
NaN is not equal to anything. The only way to confirm that something is NaN is through the function isNaN().
alert(typeof NaN); // alerts 'Number'
alert(NaN === NaN); // evaluated false
Replace() can accept callback function
This is one of JavaScript's object keep secrets and it arrived in v1.3 Most usages of replace() looks something like this:
alert('10 13 21 48 52'.replace(/\d/g, '*'));
// replace all numbers with *
This is the simple replacement: a string, an asterisk. But what if we wanted more control over how and when our replacements take place? What if we wanted to replace only the number under 3? This can't be achieved with ReGex alone. We need to jump into the callback function to evaluate each match.
alert('10 13 21 48 52'.replace(/\d/g, function(match) {
return parseInt(match) < 3 ? '*' : match;
})); ** *3 ** 48 5*
For every match made, JavaScript calls our callback function, passing the match as an argument.
Undefined can be defined
Strange as it might sound, undefined is not a reserved word in JavaScript, even though it has special meaning and is the only way to determine whether a variable is undefined.
(function() {
var undefined = 'foo';
alert(undefined, typeof undefined); // foo string
})();
An array with no keys == false(about truthy and false)
alert(new Array() == false); // evaluates true
In JavaScript, every non-boolean value has a built-in boolean flag that is called on when the value is asked to behave like a boolean. False, zero, null, undefined, empty strings and NaN all end up becoming false - not permanently, just for the given expression.
--
Thanks for Reading, If you like this post please comment😎.