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JavaScript: Control Structure: Boolean, If, Switch, Loop #JavaScript #loop #control #boolean
var foo = 5 == 6; // false
foo = "6" == 6; // true. Because the number 6 are first converted into a string
foo = "6" === 6; // false. It will also check equality of data type. Always use this operator
/*
&& (AND)
|| (OR)
! (NOT)
*/
/*Truthy and falsy data types*/
if (0) {}; //falsy. Zero is considered false
if (9) {}; //as long as it is not 0, it will be true
if ("") {}; //falsy
if (" ") {}; //as long as there's character in it, it will be true
if ([]) {}; //true
if ({}) {}; //true
if (undefined) { //undefined is false. as well as null
alert("hi");
}
if (true) {} else if {} else if {} else {};
(5 > 4) ? true : false;
var order_size = "medium";
switch (order_size) {
case "small":
alert("small");
break;
case "medium":
alert("medium");
break;
case "large":
alert("large");
break;
case "extra large":
alert("extra large");
break;
default:
alert("something else?");
}
var order_size = "medium";
switch (order_size) {
case "small":
alert("small");
break;
case "medium":
case "large":
case "extra large":
alert("medium, large, or extra large");
break;
default:
alert("something else?");
}​
var temp = 18,
msg = (temp > 10) ? "Today was warm" : "Today was cold";
// typeof is used to check the variable's type
alert(typeof null); //object
//Error protection syntax
/*Different web browsers include different properties on the error
object. but the main ones are name and message, which are the type of error and
a description of what happened, respectively. You can throw your
own errors using the throw keyword and creating an error object.
You can create this error object as an object literal, or you can use
the error constructor functions.*/
try {
// code that might cause an error here
} catch (e) {
// deal with the error here
} finally {
// do something to finalize it
}
function make_coffee(requested_size) {
var sizes = ["large", "medium", "small"],
coffee;
if (sizes.indexOf(requested_size) < 0) {
throw new Error("We don't offer that size");
}
coffee = { size: required_size,
added: ["sugar", "sugar", "cream" ]
};
return coffee;
}
try {
make_coffee("extra large");
} catch (e) {
console.log(e.message);
}​
var names = ["Jeremy", "Jeffrey", "Jackey", "Jennifer"];
for (var i = 0, length = names.length; i < length; i++) { //efficient
alert(names[i]);
};
var len = names.length,
i = 0;
while (i < len) {
i++;
}
do {
var element = names.pop();
alert(element);
} while (names.length > 0);
/*In JavaScript, running through a simple loop is a lot cheaper than calling a function multiple times.
In Essence, minimize recursive call*/
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