Javascript
Javascript is the scripting language hosted by your browser. It can automate lots of things, like manipulating the document, add/remove/modify HTML/SVG/CSS elements.
<!DOCTYPE html>
<head>
</head>
<body>
<svg height="297mm" width="210mm">
<rect class="bar" height="60" width="50" y="6" x="7" />
</svg>
<script>
document.querySelector('.bar').style.fill = 'skyblue';
</script>
</body>
</html>
A good way to learn Javascript is with the Codecademy class or the Mozilla Javascript guide.
This is the bare minimum to survive in Javascript world:
<script>
// this is a comment
// this is a variable named "foo" containing the value 1
var foo = 1;
// this is an array named "bar" containing a series of numbers
var bar = [1, 2, 3, 4];
// this is an object named "baz" containing a serie of key:value pairs
var baz = {a: 1, b: 2};
// you can access every value by key
var bazA = baz.a;
// or the equivalent
var bazA = baz['a'];
// this is a function named "aaa" expecting an argument
// and returning the value of this argument + 1
function aaa(d){
return d + 1;
}
// this is an example of how you use it
var result = aaa(2);
// and you can all use them together
var something = [{a: function(d){ return d + 'px'; }}, 10, baz.a, aaa(10)];
</script>
</html>
All of these variables, functions, arrays, strings, numbers, etc. are objects. They all have an associated object tree that looks like the DOM (in fact, there are also some primitives that are wrapped into objects). You can look at their structure same as the DOM using the Developer tools console.