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-rw-r--r--javascript.html.markdown35
1 files changed, 22 insertions, 13 deletions
diff --git a/javascript.html.markdown b/javascript.html.markdown
index acac1795..6234aebc 100644
--- a/javascript.html.markdown
+++ b/javascript.html.markdown
@@ -26,29 +26,34 @@ doStuff();
// wherever there's a newline, except in certain cases.
doStuff()
-// Semicolons are a heated topic in the JavaScript world, but they're really a
-// matter of personal or style-guide preference. We'll leave them off here.
+// We'll leave semicolons off here; whether you do or not will depend on your
+// personal preference or your project's style guide.
/***********
- * 1. Primitive Datatypes and Operators
+ * 1. Numbers, Strings and Operators
***********/
// Javascript has one number type that covers ints and floats.
3 // = 3
1.5 // = 1.5
-// which support all the operations you'd expect.
+// All the basic arithmetic works as you'd expect.
1 + 1 // = 2
8 - 1 // = 7
10 * 2 // = 20
35 / 5 // = 7
-// Uneven division works how you'd expect, too.
+// Including uneven division.
5 / 2 // = 2.5
// Enforce precedence with parentheses
(1 + 3) * 2 // = 8
+// There are three special not-a-real-number values:
+Infinity // result of e.g. 1/0
+-Infinity // result of e.g. -1/0
+NaN // result of e.g. 0/0
+
// There's also a boolean type.
true
false
@@ -70,10 +75,10 @@ false
2 != 1 // = true
// More comparisons
-1 < 10 // => True
-1 > 10 // => False
-2 <= 2 // => True
-2 >= 2 // => True
+1 < 10 // = true
+1 > 10 // = false
+2 <= 2 // = true
+2 >= 2 // = true
// Strings are concatenated with +
"Hello " + "world!" // = "Hello world!"
@@ -81,17 +86,21 @@ false
// and are compared with < and >
"a" < "b" // = true
-// You can also compare strings with numbers
+// Type coercion is performed for comparisons...
"5" == 5 // = true
-// but this is almost always not what you want, so use === to stop this
+// ...unless you use ===
"5" === 5 // = false
// You can access characters in a string with charAt
"This is a string".charAt(0)
-// There's also a null keyword
-null // = null
+// There's also null and undefined
+null // used to indicate a deliberate non-value
+undefined // used to indicate a value that hasn't been set yet
+
+// null, undefined, NaN, 0 and "" are falsy, and everything else is truthy.
+// Note that 0 is falsy and "0" is truthy, even though 0 == "0".
/***********
* 2. Variables, Arrays and Objects