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JS4Python Notes

3 min read

Description

Notes from this resource.

The Basics

  • JS built in classes:
    • Array
    • Regex
    • Date
    • Math
    • JSON
  • An interesting quote: “You might think of Python as being fairly informal. There are other languages, like Java and C++ that are more formal.”
  • The first version of JS was written in just 10 days ?!?!
  • An interesting set of ways to define functions:
    • The below definition is without hoisting, so main() cannot be called before the definition.
function main() {
    alert("Hello World!")
    writeln("Hello World!");
}
--------
var main = function() {
    alert("Hello World!")
    writeln("Hello World!");
}
  • “This example also makes it clear that in JavaScript functions are just objects that can be assigned to variables.”
  • “Now there is one more character on this line that is significant and that is the ; at the end. In JavaScript the ; signifies the end of a statement. Unlike Python where statements are almost always only one line long JavaScript statements can spread across many lines. The compiler knows it has reached the end of a statement when it encounters a ;.”
  • “For example (a,b) => a+b is the equivalent of function(a,b) { return a + b} or lambda a,b : a+b in Python.”
  • “In JavaScript, the parenthesis around the condition are required because if is technically a function that evaluates to True or False.”
  • Switch-case exists in JS, and can be used similarly to how elifs are used in Python.
  • JavaScript uses Java like notation for definite for loops: for (let i = 0; i < 10; i++) {...}
  • Two options for condensed for loops, for-of will access items in the iterable, for-in accesses the indices.
let l = [1, 2, 1, 2, 3]
for (let i of l) {
    writeln(i);
}

Output: 1 2 1 2 3

------------

let l = [1, 2, 1, 2, 3]
for(let i in l) {
    writeln(l[i]);
}

Output: 1 2 1 2 3
  • .forEach() also exists, and allows you to iterate over elements of an array
  • while and do-while loops both exist in JS, and they’re very similar to Java’s.
  • Primitive types: number, string, boolean, undefined, null, symbol
  • 3 scopes in JS: global, function, block
    • Global: Any var that is declared outside of a function, and is accessible from anywhere in code.
    • Function: Independent to each function. Variables defined within this scope are only accessible from within the function
    • Block: definitions from let statements, for example.
  • “The best advice I have seen is to stop using var and just use let in your code.”
  • JS is dynamically typed
  • User input function is prompt. This brings up a dialog box.
  • JS only has a single numeric data type. It also doesn’t support infinite precision ints.
  • Falsy values in JS (everything else evaluates to true):
    • null
    • undefined
    • NaN
    • 0
    • ""
    • false
  • JS strings are immutable, and there’s no indexing or slicing built-in operators. Instead, use methods for this, very Java-esque.
  • Formatted strings are defined with back-ticks.

Left off on 9/8 at this section: 2.7. Collections