Interview Cake
Interview Cake
Closures, scope, hoisting, the JS object model, and more.
Learn all the "gotchas" to tricky JavaScript interview questions!
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There's something tricky going on with scope in this JavaScript. Can you guess what will get logged to the console? keep reading »
There's a tricky bug in this JavaScript. Can you find it? keep reading »
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Given an array of numbers in sorted order, how quickly could we check if a given number is present in the array? keep reading »
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Given a 5-sided die, make a 7-sided die. keep reading »
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Figure out which number is repeated. But here's the catch: optimize for space. keep reading »
Figure out which number is repeated. But here's the catch: do it in linear time and constant space! keep reading »
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For each number in an array, find the product of all the other numbers. You can do it faster than you'd think! keep reading »
Find the highest possible product that you can get by multiplying any 3 numbers from an input array. keep reading »
Write a function for merging meeting times given everyone's schedules. It's an enterprise end-to-end scheduling solution, dog. keep reading »
Write code to continually track the max, min, mean, and mode as new numbers are inserted into a tracker class. keep reading »
Design a ticket sales site, like Ticketmaster keep reading »
If we execute this Javascript, what will the browser's console show?
It's not "outside".
It's not "inside".
The script won't throw an error!
The console will log undefined.
To understand this, we need to explain a few things about Javascript.
Function-level scope. Functions create new scopes in Javascript:
Blocks like if statements and for loops do not create a new scope (this is also true of Python and recent versions of Ruby, but untrue of Java and C):
Declaration vs. assignment. A variable declaration simply tells the interpreter that a variable exists. By default it initializes the variable to undefined:
A variable assignment assigns a value to the variable:
We can both declare and assign in the same line:
Hoisting. In Javascript, variable declarations are "hoisted" to the top of the current scope. Variable assignments, however, are not.
So returning to the original problem:
The declaration (but not the assignment) of text gets hoisted to the top of logIt. So our code gets interpreted as though it were:
So we have a new variable text inside of logIt that is initialized to undefined, which is what it holds when we hit our log statement.
Remember: when you declare a variable in JavaScript (using "var"), that variable declaration is "hoisted" to the top of the current scope—meaning the top of the current function or the top of the script if the variable isn't in a function.
Hoisting can cause unexpected behavior, so a good way to keep things clear is to always declare your variables at the top of the scope.
