var foo = "hello";
typeof foo !== "undefined";
var foo = "hello";
foo !== undefined
--enable-precise-memory-info
flag.
Test case name | Result |
---|---|
typeof | |
strict equal undefined |
Test name | Executions per second |
---|---|
typeof | 205327936.0 Ops/sec |
strict equal undefined | 18608850.0 Ops/sec |
Let's break down the benchmark and explain what's being tested.
Benchmark Overview
The benchmark is comparing two approaches to check if a variable is not defined or equal to a specific value:
typeof foo !== "undefined"
(using typeof
)foo !== undefined
(using strict equality)Options Compared
These are two different ways to express the same idea: checking if a variable is not defined.
typeof foo !== "undefined"
uses the typeof
operator, which returns a string indicating the type of the variable. If the variable is undefined, typeof
returns "undefined"
. This approach is commonly used in JavaScript to check if a variable has been declared.foo !== undefined
uses strict equality (!==
) with no quotes around "undefined"
, which is considered an invalid syntax in most JavaScript implementations. However, some browsers (like Chrome) may still interpret it correctly due to a quirk.Pros and Cons of Each Approach
typeof foo !== "undefined"
foo !== undefined
(invalid syntax)Library and Special JS Feature
There is no library involved in this benchmark. However, it's worth noting that the typeof
operator relies on a feature of the JavaScript language called "type checking" or "type inference," which was introduced in ECMAScript 3 (ES3).
Other Considerations
When writing JavaScript code, it's essential to consider the nuances of type checking and equality checks. The benchmark highlights an important distinction between typeof
and strict equality (!==
). While both approaches can be used to check for undefined values, using typeof
is generally considered more reliable due to its wider support.
Alternatives
If you're interested in exploring alternative ways to check for undefined values or perform type checking, consider the following options:
instanceof
operator with a constructor function to check if an object is of a specific type.isUndefined()
function or TypeScript's any
type to simplify type checking.In summary, the benchmark is testing two approaches to check if a variable is not defined: using typeof
and strict equality. While both methods have their trade-offs, typeof
is generally considered more reliable due to its widespread support across browsers.