In this case, JavaScript, being the dynamic and weakly-typed language it is, will merely default to an undefined value rather than raise an error. It is typically encountered when attempting to access a value where no value exists. There are a number of ways of yielding an undefined value in code. The difference between the two is perhaps a bit more clear through code: let a console. null is a variable that is defined but is missing a value. This Is Why Andreas Sujono Top 10 Tricky Javascript Questions often asked by Interviewers Christopher Clemmons in Level Up Coding 9. To distinguish between the two, you may want to think of undefined as representing an unexpected absence of value and null as representing an expected absence of value. undefined is a variable that refers to something that doesn't exist, and the variable isn't defined to be anything. JavaScript in Plain English Coding Won’t Exist In 5 Years. This is an important distinction both serve different purposes and justifiably so. Comparing the two with a strict equality operator ( =), which equates both value and type, is enough to prove that: undefined = null // false Each serve as the sole member of its own distinct type undefined is of type Undefined and null is of type Null. Comparing the two with other falsy values using an equality operator ( =) reveals that they are not equal to anything except themselves: null = 0 // falseĭespite this and the other similarities, null and undefined are not equivalent. The absence of value lends to their characterization as falsy values, meaning they evaluate to false when employed in the context of a conditional, such as an if statement. They are, as their names suggest, completely void of value. In fact, attempting to access or define a property will raise a TypeError. Both are completely immutable, have no properties or methods, and are incapable of property assignment. In other words, it’s an indication of “no value.” While similar, undefined actually represents the non-existence of a value. undefined 'data' But that is not the case anymore. In JavaScript, null is a literal and language keyword that represents no discernible object value. This article, however, will be focusing on the more unique primitive data types known as Null and Undefined what makes them similar, dissimilar, and overall unusual. These primitives are fairly straightforward and function as you might expect. When discussing primitive data types in JavaScript, most people are aware of the basics, starting with String, Number, and Boolean. Javascript Programming Discussion Live Q/A Session
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