关键字中的JavaScript对象冒号

Question

Enclosed a screenshot of the Javascript console (Chrome Version 36.0.1985.125 m) after executing:

console.log(node)
console.log(node['read_cam0:x'])
console.log(node['label'])

Why is node["read_cam0:x"] undefined?

added issue at sigma.js: https://github.com/jacomyal/sigma.js/issues/361

UPDATE: Firefox console shows this:

see the read_cam0 missing from the object on the left but displayed on the right (after clicking on object on the left side).

Answer 1

The expression obj["read_cam0:x"] works as you would expect and is not undefined .

The return value of console.log() is always undefined (therefore the second line in your screenshot). However, calling the function has the side-effect that it logs stuff to the console (the first line line in your screenshot).

Entering console.log in the Chrome dev-console (as opposed to executing it in a javascript file) thus always results in two lines:

Answer 2

Obviousely the chrome console shows the object in it's updated state while a line below it logs the state before the object was updated. The problem was identified by using a setTimeout .

Answer 3

This just means the object you are trying to print to the console is undefined. The output would be [Object object] if it existed

Answer 4

read_com0 is an object

Try this:

console.log(node)
console.log(node["read_cam0"]["x"])