Modern JS should be written in strict mode which bans implicit globals (preferring to explicitly declare them at the top level instead, thus prevent accidental globals when a variable name is typoed). Yes, you should always use var .
Omitting var updates an existing variable. There are two caveats to this: If a variable is already defined in the current scope, prefixing it with var will throw an error. If a variable isn’t currently defined, omitting var creates a new variable (you should always use var to define a new variable, though).
Is var bad in JS?
Why VAR is not recommended?
Should I use VAR or let?
The main difference between the two though is that let deals with block scope whereas var deals with global scope or function scope depending on where it’s declared. As long as your variable isn’t declared within any function, var can be used again anywhere else in your code.
Is Infinity a JS?
The isFinite() function determines whether a number is a finite, legal number. This function returns false if the value is +infinity, -infinity, or NaN (Not-a-Number), otherwise it returns true.
How do you remove the property name from this object?
The delete operator is used to remove these keys, more commonly known as object properties, one at a time. The delete operator does not directly free memory, and it differs from simply assigning the value of null or undefined to a property, in that the property itself is removed from the object.
var is optional. var puts a variable in local scope. If a variable is defined without var , it is in global scope and not deletable.