Add string operator resources (#2133)

* Adding arguments-object

* Adding string-operators

* Update content/roadmaps/106-javascript/content/108-javascript-expressions-and-operators/106-string-operators.md

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

content/roadmaps/106-javascript/content/108-javascript-expressions-and-operators/106-string-operators.md

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-# String operators
+# String Operators
+
+Strings are useful for holding data that can be represented in text form. Some of the most-used operators on strings are to build and concatenate them using this string operators: `+` (Concatenate), `+=` (Concatenate Assignment).
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Expressions_and_Operators#string_operators'>Arithmetic Operators - MDN</BadgeLink>
+<BadgeLink colorScheme='yellow' badgeText='Read' href='https://javascript.info/operators#string-concatenation-with-binary'>String Concatenation - JavaScript.info</BadgeLink>

content/roadmaps/106-javascript/content/109-javascript-functions/104-arguments-object.md

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 # Arguments object
+
+The arguments object is an Array-like object accessible inside functions that contains the values of the arguments passed to that function, available within all non-arrow functions. You can refer to a function's arguments inside that function by using its arguments object. It has entries for each argument the function was called with, with the first entry's index at 0. But, in modern code, rest parameters should be preferred.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+
+<BadgeLink colorScheme="yellow" badgeText="Read" href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/arguments">The arguments object - MDN Docs</BadgeLink>