A keyword is a reserved word which has a special meaning in JavaScript. See also word operators if this page fails to list the word which you are interested in.
break
Used to exit loops, switch...case statements and labeled block statements.
case
Necessarily organizes switch...case statements. (It can technically be omitted, but this renders the entire statement useless.)
catch
Necessarily extends try...catch statements to handle errors.
continue
Exits single iterations of loops.
default
Further organizes switch...case statements.
do
Begins do...while loops.
else
Optionally extends if statements.
false
A Boolean constant which represents falsehood.
finally
Optionally extends try...catch statements to execute commands regardless of whether any error was thrown in the try block and whether any errors remained uncaught.
for
Begins for loops.
goto
Enters labeled blocks from anywhere.
if
Begins if statements.
return
Used within functions to exit the function and set the value of the function call.
switch
Begins switch...case statements.
this
An immutable variable used inside methods to reference the owning objects. See this (computer science).
true
A Boolean constant which represents truth.
try
Begins try...catch statements.
var
Declares a variable in anticipation of its use to prevent certain scoping issues involving functions.
var x;
x is undefined.
while
Begins while loops and ends do...while loops.
with
Begins with statements.