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Taig Mac Carthy
8,139 PointsWhy is he not defining the variable inside the for in loop?
This is what I did:
for (var prop in book) {
console.log( prop + ": " + book[prop])
}
Since the variable prop is not previously defined, I had understood from this course that you had to add var inside the for in lop. However, his solution was:
for (book_property in book) {
console.log( book_property + ": " + book[book_property])
}
Without the var. Would someone please be kind enough to explain?
1 Answer
Steven Parker
229,732 PointsThis is what is called "implicit global declaration". While allowed by the syntax, it is not considered good programming practice and was probably not intended by the instructor (but easily overlooked because it did not generate an error).
You can guard against this by putting the interpreter into "strict" mode where implicit declarations are not allowed and will cause an error.
To use "strict" mode, place a line like this at the beginning of the program:
"use strict"; // put interpreter into strict mode
Taig Mac Carthy
8,139 PointsThis is very insightful, thanks so much Steven.
Zachary Smith
Full Stack JavaScript Techdegree Graduate 16,616 PointsIs this an example of implicit global declaration or am I misunderstanding? "Prod" is not defined and I guess it is "implied" that the function should pull from that object since its the only one that exists?
function addInventory(prod, val) {
prod.inventory += val;
console.log(val + " " + prod.name + "s added to the inventory.");
console.log(prod.inventory + " " + prod.name + "s in stock.");
}```
But what if I make another object? How would the function know to pull data from the correct object unless the variables are defined?
Steven Parker
229,732 PointsThere are no variable declarations (implicit or otherwise) in this example. Both "prod" and "val" are parameters.
Zachary Smith
Full Stack JavaScript Techdegree Graduate 16,616 PointsGot it, thanks so much.
Namubiru Ephrance
836 PointsNamubiru Ephrance
836 PointsJavaScript allows variable declaration without var keyword however, ou must assign a value when you declare a variable without var keyword. Now, this is not recommended because It can accidentally overwrite an existing global variable. I don't know if that helps.