JavaScript programs can be inserted into any part of an HTML document with the help of the <script><\/code> tag.<\/p>\n\n\n\n
For instance:<\/p>\n\n\n\n
<!DOCTYPE HTML>\n<html>\n\n<body>\n\n <p>Before the script...<\/p>\n\n <script>\n alert( 'Hello, world!' );\n <\/script>\n\n <p>...After the script.<\/p>\n\n<\/body>\n\n<\/html><\/code><\/pre>\n\n\n
alert(\"Thanks for your input!\");\n<\/pre>\n
Let’s say my name is Mark, and I want to store this information in the browser.<\/p>\n
A variable is created when you write var (for variable) followed by the name that you choose to give it. It takes on a particular value when you assign the value to it. This is a JavaScript statement that creates the variable name and assigns the value “Mark” to it<\/p>\n
var name = \"Mark\";<\/pre>\n
Now the variable name refers to the text string “Mark”. Note that it was my choice to call it name. I could have called it myName, xyz, lol, or something else. It’s up to me how to name my variables, within limits.<\/p>\n
name refers to “Mark”. Then I come along and code the line…<\/p>\n
name = \"Ace\";\n<\/pre>\n
Before I coded the new line, if I asked JavaScript to print name, it printed… Mark But that was then. Now if I ask JavaScript to print name, it prints… Ace<\/p>\n
Alerting the name variable!<\/p>\n
alert(name);<\/pre>\n
What do the quotes mean, and what happens if I omit the quotes? The syntactic difference between variables and text strings is that variables are never enclosed in quotes, and text strings are always enclosed in quotes.<\/p>\n
A string isn’t the only thing you can assign to a variable. You can also assign a number.<\/p>\n
var weight = 150;\n<\/pre>\n
Having coded the statement above, whenever you write weight in your code, JavaScript knows you mean 150. You can use this variable in math calculations. If you ask JavaScript to add 25 to weight…<\/p>\n
var newWeight = weight + 25;\nalert(newWeight); \/\/ will say 175<\/pre>\n
JavaScript can also handle an expression made up of nothing but variables. For example<\/p>\n
suppose you wanted to personalize a message. In another part of your code you’ve asked the user for her name and assigned the name that she entered to a variable, userName. (You don’t know how to do this yet. You’ll learn how in a subsequent chapter.) Now, you want to combine her name with a standard “Thanks” to produce an alert that says, for example, “Thanks, Susan!” When the user-provided her name, we assigned it to the variable userName. This is the code.<\/p>\n
alert(\"Thanks, \" + userName + \"!\");<\/pre>\n
Using the plus operator, the code combines\u2014concatenates\u2014three elements into the message: the string “Thanks, ” plus the string represented by the variable userName plus the string “!” Note that the first string includes a space. Without it, the alert would read, “Thanks,Susan!”. You can concatenate any combination of strings and variables, or all strings or all variables. For example, I can rewrite the last example this way<\/p>\n
![\"\"](\"http:\/\/ucsbwebdev.local\/wp-content\/uploads\/2019\/01\/image-2-1024x857.png\")
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