Q161. What is isNaN?
The isNaN() function is used to determine whether a value is an illegal number (Not-a-Number) or not. i.e, This function returns true if the value equates to NaN. Otherwi...
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Q162. How do you programmatically navigate using React Router v4?
There are three different ways to achieve programmatic routing/navigation within components. 1. **Using the `withRouter()` higher-order function:** The `withRouter()` hig...
Q163. What are the differences between undeclared and undefined variables?
Below are the major differences between undeclared(not defined) and undefined variables, | undeclared | undefined | | ----------------------------------------------------...
Q164. How to get query parameters in React Router v4?
The ability to parse query strings was taken out of React Router v4 because there have been user requests over the years to support different implementation. So the decis...
Q165. What are global variables?
Global variables are those that are available throughout the length of the code without any scope. The var keyword is used to declare a local variable but if you omit it ...
Q166. Why you get "Router may have only one child element" warning?
You have to wrap your Route's in a `` block because `` is unique in that it renders a route exclusively. At first you need to add `Switch` to your imports: ```javascript ...
Q167. What are the problems with global variables?
The problem with global variables is the conflict of variable names of local and global scope. It is also difficult to debug and test the code that relies on global varia...
Q168. How to pass params to `history.push` method in React Router v4?
While navigating you can pass props to the `history` object: ```javascript this.props.history.push({ pathname: "/template", search: "?name=sudheer", state: { detail: resp...
Q169. What is NaN property?
The NaN property is a global property that represents "Not-a-Number" value. i.e, It indicates that a value is not a legal number. It is very rare to use NaN in a program ...
Q170. How to implement _default_ or _NotFound_ page?
A `` renders the first child `` that matches. A `` with no path always matches. So you just need to simply drop path attribute as below ```jsx harmony ```