2.2 Property Access (Objects)

>>>

var o = { key: 'value' }

>>>

o.key

"value"

The . dot operator is used to access a property in an object.

>>>

o['key']

"value"

The array index syntax can also be used to access a property in an object. This syntax must be used when the property name contains spaces or non alphanumeric characters.

>>>

var propName = 'key'

>>>

o[propName]

"value"

The index syntax is also used when the property name is dynamic or stored in a variable

>>>

o.text = 1

New properties are added with assignment, using either of the two access syntaxes above.

>>>

o.doesNotExist

undefined

It is not an error to access a property that doesn't exist.

>>>

delete o.text

true

The delete operator removes properties (or global variables).

>>>

The console allows you to interact with the course material and examples. Use the following keys:

<Enter> — Execute the code
<Shift + Enter> — Add line break
<Arrow-Up> — Previous command in history
<Arrow-Down> — Next command in history

A special logging function is also available:

print(value) — Prints a value to the console.
print(value, true) — Prints a debug version of a value.

Console Learner — An interactive JavaScript course.