My reading journal for Code Fellows.
There are many different operators in JavaScript and they all do something different.
An assignment operator assigns a value to its left operand based on the value of its right operand. The simple assignment operator is =, which assigns the value of its right operand to its left operand. That is, x = f() is an assignment expression that assigns the value of f() to x.
If a variable refers to an object, then the left-hand side of an assignment expression may make assignments to properties of that variable.
A comparison operator compares its operands and returns a logical value based on whether the comparison is true. The operands can be numerical, string, logical, or object values. In most cases, if the two operands are not of the same type, JavaScript attempts to convert them to an appropriate type for the comparison. This behavior generally results in comparing the operands numerically. The sole exceptions to type conversion within comparisons involve the === and !== operators, which perform strict equality and inequality comparisons. These operators do not attempt to convert the operands to compatible types before checking equality.
An arithmetic operator takes numerical values (either literals or variables) as their operands and returns a single numerical value. The standard arithmetic operators are + - * /. These operators work the same as you would normally use them with a calculator.
A bitwise operator treats their operands as a set of 32 bits (zeros and ones), rather than as decimal, hexadecimal, or octal numbers. For example, the decimal number nine has a binary representation of 1001. Bitwise operators perform their operations on such binary representations, but they return standard JavaScript numerical values.
Logical operators are typically used with Boolean (logical) values; when they are, they return a Boolean value. However, the && and || operators actually return the value of one of the specified operands, so if these operators are used with non-Boolean values, they may return a non-Boolean value.
In addition to the comparison operators, which can be used on string values, the concatenation operator
+ concatenates two string values together, returning another string that is the union of the two operand strings.
let username = Jim
alert("Hello" + username); //This sends a browser message saying "Hello Jim".
The conditional operator is the only JavaScript operator that takes three operands. The operator can have one of two values based on a condition. If the condition is true, the operator has the value of val1. Otherwise it has the value of val2. You can use the conditional operator anywhere you would use a standard operator.
condition ? val1 : val2
The comma operator , evaluates both of its operands and returns the value of the last operand. This operator is primarily used inside a for loop, to allow multiple variables to be updated each time through the loop. It is regarded bad style to use it elsewhere, when it is not necessary. Often two separate statements can and should be used instead.
A unary operation is an operation with only one operand. A very simple example is using delete.
delete object.property;
A relational operator compares its operands and returns a Boolean value based on whether the comparison is true.
The in operator returns true if the specified property is in the specified object.
propNameOrNumber in objectName
Where propNameOrNumber is a string, numeric, or symbol expression representing a property name or array index, and objectName is the name of an object.
Loops offer a quick and easy way to do something repeatedly. There are many different kinds of loops, but they all essentially do the same thing: they repeat an action some number of times.
A for loop repeats until a specified condition evaluates to false.
for ([initialExpression]; [conditionExpression]; [incrementExpression])`
statement
The following steps occur when you execute a for loop:
initialExpression, if any, is executed. This expression usually initializes one or more loop counters, but the syntax allows an expression of any degree of complexity. This expression can also declare variables.conditionExpression expression is evaluated. If the value of conditionExpression is true, the loop statements execute. Otherwise, the for loop terminates. If the conditionExpression expression is omitted entirely, the condition is assumed to be true.statement executes. Multiple statements can be executed by using a block statement to group them.incrementExpression is executed.A while statement executes its statements as long as a specified condition evaluates to true.
while (condition)
statement
If the condition becomes false, statement within the loop stops executing and control passes to the statement following the loop.
The condition test occurs before statement in the loop is executed. If the condition returns true, statement is executed and the condition is tested again. If the condition returns false, execution stops, and control is passed to the statement following while.
Multiple statements can be executed by using a block statement to group them.
The do-while statement repeats until a specified condition evaluates to false.
do
statement
while (condition);
statement is always executed once before the condition is checked.
If condition is true, the statement executes again. At the end of every execution, the condition is checked. When the condition is false, execution stops, and control passes to the statement following do...while.
Use the break statement to terminate a loop, switch, or in conjunction with a labeled statement.
break without a label, it terminates the innermost enclosing while, do-while, for, or switch immediately and transfers control to the following statement.break with a label, it terminates the specified labeled statement.break;
break [label];