JavaScript Basics - Stanford University
JavaScript Basics
Mendel Rosenblum
CS142 Lecture Notes - JavaScript Basics
1
What is JavaScript?
From Wikipedia:
... high-level, dynamic, untyped, and interpreted programming language
... is prototype-based with first-class functions, ¡
... supporting object-oriented, imperative, and functional programming
... has an API for working with text, arrays, dates and regular expressions
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Not particularly similar to Java: More like C crossed with Self/Scheme
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C-like statements with everything objects, closures, garbage collection, etc.
Also known as ECMAScript
CS142 Lecture Notes - JavaScript Basics
2
Some thoughts about JavaScript
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Example of a scripting language
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Seems like it was designed in a rush
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"use strict"; tweaks language to avoid some problematic parts
Language being extended to enhance things: New ECMAScript every year!
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Some ¡°Good Parts¡±, some not so good
Got a bad reputation
Many programmers use a subset that avoids some common problems
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Interpreted, less declaring of things, just use them (popular today: e.g. python)
Transpiling common so new features used: e.g ECMAScript Version N, TypeScript
Code quality checkers (e.g. jslint, jshint, eslint) widely used
CS142 Lecture Notes - JavaScript Basics
3
Good news if you know C - JavaScript is similar
i = 3;
i = i * 10 + 3 + (i / 10);
while (i >= 0) {
sum += i*i;
// Comment
i--;
}
for (i = 0; i < 10; i++)
}
/* this is a comment */
{
if (i < 3) {
i = foobar(i);
} else {
i = i * .02;
}
Most C operators work:
* / % + - ! >= < && || ?:
function foobar(i) { return i;}
continue/break/return
CS142 Lecture Notes - JavaScript Basics
4
JavaScript has dynamic typing
var i;
// Need to define variable ('use strict';), note: untyped
typeof i == 'undefined'
i = 32;
// It does have a type of ¡®undefined¡¯
// Now: typeof i == typeof 32 == 'number'
i = "foobar"; // Now: typeof i == typeof 'foobar' == 'string'
i = true;
// Now typeof i == 'boolean'
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Variables have the type of the last thing assigned to it
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Primitive types: undefined, number, string, boolean, function, object
CS142 Lecture Notes - JavaScript Basics
5
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