JavaScript Variables Worksheet

Snippet | Expression | Answer | Explanation |
---|---|---|---|

1 | 100+4 | 104 | basic addition |

2 | 'a'+'b' | 'ab' | Concatenation of strings |

3 | 'Bob'+'Smith' | 'BobSmith' | Concatenation of strings |

4 | '7'+'9' | '79' | Concatenation of strings |

5 | '7'+9 | '79' | Concatenation of strings, as JS treats the number like a string here |

6 | '7'-9 | -2 | Because the minus symbol is special to arithmetic functions, this treated as a numerical value |

7 | 'abc'*3 | NaN | The multiplication operator wants to treat all parts of the expression as a number which is not possible - Not a Number |

8 | 7+2*3 | 13 | Order of operations |

9 | (7+2)*3 | 27 | Order of operations |

10 | (null+2)/3 | 0.6666666666666666 | Order of operations "null" has no value, so evaluation continues after that expression |

11 | var name;
name |
undefined | The variable "name" holds no value |

12 | var x = 7;
var y = 4; var z = x * y; z-3 |
25 | Logical math through use of variables |

13 | var a = true;
var b = false; a && b |
false | Both condition must be met to be True |

14 | var a = true;
var b = false; a || b |
true | If either condition is True, then the statement evaluates to True |

15 | var foo = 3;
foo++; foo++; foo/2 |
2.5 | Variable "foo" is incremented two times and then divided |

16 | var age = 29.8;
var wholeAge = Math.floor(age); var nextAge = Math.ceil(age); nextAge - wholeAge |
1 | Variable age is rounded up then down to evaluate |

17 | '5' + 3 - 3 | 50 | First part of expression is concatenated, then subtraction treats the expression as a number |

18 | var isRed = false;
isRed = !isRed; isRed |
true | The use of the "!" (bang) character switches the value to the opposite |

19 | var isBlue = true;
var isBlue = !!isBlue; isBlue |
true | Double bang makes the variable isBlue false and then true. Not extremely useful. |

20 | var name = 'Sally';
var age = 25; name.length + age |
30 | Length of string added to a number |

21 | var x = 10;
var y = 73.3; var point = '[' + x + ', ' + y + ']'; 'point: '+point |
'point: [10, 73.3]' | Variables inserted into a string variable (that mimics an array) |

22 | var numberOfSheep = 16;
var numberOfGoats = 3; numberOfGoats + numberOfSheep++ |
19 | The evaluation of the values inside the variables occurs before the "++" increment expression can be stored and used |

23 | var numberOfSheep = 16;
var numberOfGoats = 3; numberOfGoats - ++numberOfSheep |
-14 | The increment expression is before variable so it is evaluated before the numberOfSheep variable is already used |

24 | var x;
var y = (x=7); y |
7 | Logical, just follow the parentheses |