If you’re in the global scope, there’s not much difference. Read Kangax’s answer for explanation
If you are in a function, then var will create a local variable, “without var” will look up the scope chain until it finds the variable or reaches the global scope (at which point it will create it)
There is a difference .
var x = 1 declares variable x in the current scope (aka execution context). If the declaration appears in a function – a local variable is declared; if it is in the global scope – a global variable is declared.
x = 1 on the other hand, it’s just an attribute assignment. It first tries to resolve the x scope chain. If it finds it anywhere in that scope chain, it does the assignment; if it doesn’t find x , then it just creates the property on the global object (which is the top-level object in the scope chain) . x
Now, notice that it doesn’t declare a global variable, it creates a global property.
The difference between the two is subtle and can be confusing unless you understand that variable declarations also create properties (only on variable objects) and Javascript
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