reading-notes

Expressions of a 30 Something JS Function…Or Do Operators still answer the call?

Two types of expressions:

Side Effects - such as assigning values

• x = 7
• operator is = and assigns the value 7 to the variable x

Purely Evaluate

• 3 + 4
• uses the + operator to add 3 and 4 to produce the value 7
• however, this must become part of a bigger construct (variable declaration such as const z = 3 + 4) or its result will be immediately discarded

JS Operators (JS O)

• Assignment Operator
  • = assigns a value to a variable
  • ex let x = 10; assigns a value of 10 to variable x
  • + adds numbers
  • * multiplication operator
• biary operator ex: operand1 operator operand2
• unary operator ex: operator operand OR operand operator

Types of Operators

• Arithmetic perform arithmetic
• Assignment assign values to JS variables
• Comparison greater than, less tahn, equal to, not equal to
• String comparison operators used on strings; strings are compared alphabetically

• Logical *&& logical and;

  logical or; ! logical not*

• Bitwise work on 32 bit numbers; any numeric operand in the operation is converted into a 32 bit number. Result is converted back to a JS number
• Ternary
• Type returns variable type or returns true if an object is an instance of an object type; typeof or instanceof

Assigning to Properties

• Does the expression evaluate an object? Then the left-hand side of an assignment expression may make assignments to properties of that expression
• EX: const obj = {}; -> obj.x = 3; console.lob(obj.x); // prints 3 or console.log(obj); // prints x: 3.

• EX: const key = "y"; obj[key] = 5; console.log(obj[key]); // prints 5. console.log(obj); // prints { x: 3, y: 5 }

• Destructuring is for more complex assignments and makes it possible to extract data from arrays or objects using a syntax that mirrors the construction of array and object literals (see below)

For Statement

• for loop repeats until a specified condition evals to false. JS loop is similar to Java and C loop
• for statements look as follows:

When a for loop executes the folloing occurs

• initializing expression initialization, if any, is executed. This ususally initializes one or more loop counters, but the syntax allows an expression of any degree of complexity. Can also declare variables
• condition expression is evaluated. If the value of condition is true, the loop statement executes. Otherwise, for loop terminates. If condition expression is omitted entirely then condition is assumed to be true
• statement executes. To execute multiple statements, use a block statement ({}) to group those statements
• If present, the update expression afterthought is executed
• control returns to step 2
• EXAMPLE

While Statement

• a while statement executes its statements as long as a specified condition evaluates to true. A while statement looks like
• while (condition) statement
• if the condition becomes false, statement within the loop stops executing and control passes to the statement following the loop
• condition test occurs before statement in the loop is executed. If condition returns true, statement is executed and the condition is tested again. If the condition returns false, execution stop, and control is passed to the statement following while.
• to execute multiple statements, use a block statement ({}) to group those statements 1whileloop