JavaScript Logic Operators Notes

First of all, we have to know which values are considered false in JavaScript. Basicly, everything in JavaScript is treated as true expect

• false(boolean value)
• null/undefined
• 0/NaN
• ’’(empty string)

With the above fundamental background, now we can take a look at how lazy JavaScript works.
Rules:

• JavaScript always tries to return the value itself, no matter it is a String, Object, Number or Boolean, instead of just returning the Boolean number.
• True && x = x
  If the first value is true(or other values treated as true), then the first value is irrelevant. Thus return the second value since the result is only determined by x.
• False/null/0/NaN/’’ && x = false/null/0/NaN
  The second value is irrelevant, just give me the first value
• False/null/0/NaN/’’ || x = x
  Similar to the second rule, in this case, first value never counts.
• True || x = True
  Note that true can be any value that are treated as true here. The return value will always be the same as the first value.

Exercise