Some Javascript

• Activate the console (ctrl-shift-j in chrome)
• I try to start all javascript with 'use strict'

  • <script type="text/javascript">
    'use strict'
    </script>

  • reference.
  • It does many things, but the most important is to eliminate undeclared variables.
• Javascript is very c-like

  • <script type="text/javascript">
    console.log("5+3 = ", 5+3);
    console.log("5/3 = ", 5/3);
    console.log("5%3 = ", 5%3);
    console.log("0/0 = ", 0/0);
    </script> 

• Strings
  • Strings can be in single or double quotes.
  • There really is no character type, just strings.
  • concatenation is +
  • newline is '\n' or "\n"
  • escape is \ just like in c
  • If you put strings in `, anything inside ${} will be evaluated

  • <script type="text/javascript">
    console.log ("Hello World");
    console.log ('This is Dan\'s string');
    console.log ("This is Dan's string");
    console.log ('See, I can put "quotes" in a string');
    console.log ("A\ncouple\nof\nlines\n");
    console.log(`The sum of 3 and 2 is ${3+2}`);
    console.log("But it is also "+(3+2));
    </script> 

• Boolean
  • Boolean values are true and false.
  • && for and, the keyword and is not recognised
  • || for or, the keyword or is not recognised
  • ! for not.
  • Most comparison operators ar the same.
  • == is comparison but...
    • == does a type cast if the types are different
    • === compares Direct comparison of values.

  • <script type="text/javascript">
    let i = 1;
    let j = "1";
    let k = 31;
    console.log("i = " , i);
    console.log("j = " , j);
    console.log("k = " , k);
    console.log("i == j " , i == j);
    console.log("i === j " , i === j);
    console.log("j == k " , k == k);
    console.log("j === k " , k === k);
    </script>

• Empty Values are undefined
  • undefined is a value, and can be used in comparison
  • typeof will return the type of anything.

  • <script type="text/javascript">
    let notUsed;
    console.log("notUsed === undefined", notUsed === undefined);
    console.log("notUsed is of type ",typeof(notUsed));
    console.log("i is of type ", typeof(i));
    console.log("j is of type ", typeof(j));
    console.log("k is of type ", typeof(k));
    console.log("true is of type ", typeof(true)); 
    </script>