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JavaScript Introducing the Practice

Samuel Kleos
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Samuel Kleos
Front End Web Development Techdegree Student 12,719 Points

What if . . . πŸ€” I nested the `i` assignment inside another function. Why on earth does this work as a solution!?

Ok so of course I fixed the loop to scope i inside the block as a let rather than a var.

But then I moved the assignment of the other i INSIDE the addNewTeachers function.

How/why is another i being assigned when it was never declared?

const courses = [
  'Introducing JavaScript',
  'JavaScript Basics',
  'JavaScript Loops, Arrays and Objects',
  'Getting Started with ES2015',
  'JavaScript and the DOM',
  'DOM Scripting By Example'
];



function addNewTeachers(newTeachers) {
  i = courses.length; // ❓ I moved `i` here from the global scope but I NEVER DECLARED IT
  newTeachers.forEach((newTeacher) => {
    teachers.push({name: newTeacher.name, topicArea: newTeacher.topicArea});
  });
}
addNewTeachers(newTeachers)



function printTreehouseSummary() {
  for (let i = 0; i < teachers.length; i++) {
     console.log(`${teachers[i].name} teaches ${teachers[i].topicArea}`);
    }
  console.log(`Treehouse has ${i} JavaScript courses, and ${teachers.length} Javascript teachers`);
  // ❓How on earth does it have access the correct value (6) here??
}


printTreehouseSummary();

CORRECT CONSOLE OUTPUT:

Ashley teaches Javascript                                                                                     
James teaches Javascript                                                                                      
Treasure teaches Javascript                                                                                   
Treehouse has 6 JavaScript courses, and 3 Javascript teachers  

1 Answer

Brian Jensen
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STAFF
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Brian Jensen
Treehouse Staff

Great question Samuel Kleos! :star:

By default, if you assign a value to a variable that you have not declared, JavaScript implicitly declares that variable for you. Implicitly declared variables are always created as global variables, even if they are used within the body of a function.

However, if you enable strict mode by adding "use strict" to the top of your JS file, it will disable that behavior and throw this error:

ReferenceError: i is not defined