To assign a value to a variable is very simple just do it this way
var foo = "bar";
But to assign a name to the variable (dynamically) as you have to do?
var variableName = "newName";
var variableName = "bar"; // in this case assign new value of variableName
Do I have to do it this way?
var foo + "_" + variableName = "foo" // foo_newName = "bar"
You can make dynamic variable using this way
window['varname'] = "test";
alert(varname);
You can do that by using eval(), but there are some Reservations about using that method:
eval("foo_" + i + "='bar'")
As per my understanding, you can not create variables like this, however, you can use object and set its property.
var foo = "bar";
var variableName = "newName";
window[foo + "_" + variableName] = "foo" ;
console.log(bar_newName);
or
var foo = "bar";
var variableName = "newName";
var obj = {};
obj[foo + "_" + variableName] = "foo" ;
console.log(obj["bar_newName"]);
window, if you like), but not local variables.