3 ms·

matcher: function (item) { return ~item.toLowerCase().indexOf(this.query.toLowerCase()) } Why there is "~" bitwise operator used in this method?

voyou 14y ago
indexOf returns -1 if the query isn't found in the string; -1 is usually represented as all bits 1, so a bitwise not on -1 is 0, which when converted to a Boolean is false. So ~x is more-or-less equivalent to x != -1; but its a bit obscure, and seems like bad style to me (indeed, I'm not even sure if the ECMAScript standard guarantees that -1 is stored as all bits 1, so it may not even by correct).
- ahoge 14y ago
  Numbers are IEEE 754 floating point. It's a separate standard which they just had to reference. I do agree that it's bad style, because it doesn't clearly communicate the intention. If you want something that returns true or false, you should return true or false.
  - voyou 14y ago
    Yeah, but -1 isn't represented in IEEE 754 floating point as all bits one, is it? The ECMAScript standard specifies that the bitwise operators work by first converting their arguments to 32-bit signed integers, but at least how I read it, it doesn't actually say anything about how these 32-bit signed integers are represented (which implies that they continue to be represented as IEEE 754, which isn't how browsers behave, and wouldn't be very useful).
    - deafbybeheading 14y ago
      It's not. And you're right, the spec isn't clear. On the other hand, the current behavior of pretending the bits are arranged in 32-bit two's-complement fashion for appropriate integer values when applying bitwise operators is really the only sensible interpretation (especially since a 64-bit float can represent all 32-bit ints).
ahoge 14y ago
It turns -1 (indexOf's "not found" result) into 0 (i.e. something falsy). Any other value is turned into something which isn't 0 (i.e. something truthy). Basically, it's a smug version of: return item.toLowerCase().indexOf(this.query.toLowerCase()) !== -1; Writing it like this is a lot clearer. Furthermore it even returns `true` and `false` instead of some truthy/falsy integer.
kevincennis 14y ago
`indexOf` returns -1 if there's no match. Bitwise NOT on -1 will give you 0 -- for any other number, it'll return a truthy value. It's the same as: `return item.toLowerCase().indexOf(this.query.toLowerCase()) !== -1` If you're really dead set on doing things this way, it's safer to prefix with !! to coerce a real boolean: `return !!~item.toLowerCase().indexOf(this.query.toLowerCase())`

voyou 14y ago

indexOf returns -1 if the query isn't found in the string; -1 is usually represented as all bits 1, so a bitwise not on -1 is 0, which when converted to a Boolean is false. So ~x is more-or-less equivalent to x != -1; but its a bit obscure, and seems like bad style to me (indeed, I'm not even sure if the ECMAScript standard guarantees that -1 is stored as all bits 1, so it may not even by correct).

ahoge 14y ago
Numbers are IEEE 754 floating point. It's a separate standard which they just had to reference. I do agree that it's bad style, because it doesn't clearly communicate the intention. If you want something that returns true or false, you should return true or false.
- voyou 14y ago
  Yeah, but -1 isn't represented in IEEE 754 floating point as all bits one, is it? The ECMAScript standard specifies that the bitwise operators work by first converting their arguments to 32-bit signed integers, but at least how I read it, it doesn't actually say anything about how these 32-bit signed integers are represented (which implies that they continue to be represented as IEEE 754, which isn't how browsers behave, and wouldn't be very useful).
  - deafbybeheading 14y ago
    It's not. And you're right, the spec isn't clear. On the other hand, the current behavior of pretending the bits are arranged in 32-bit two's-complement fashion for appropriate integer values when applying bitwise operators is really the only sensible interpretation (especially since a 64-bit float can represent all 32-bit ints).

ahoge 14y ago

It turns -1 (indexOf's "not found" result) into 0 (i.e. something falsy). Any other value is turned into something which isn't 0 (i.e. something truthy). Basically, it's a smug version of: return item.toLowerCase().indexOf(this.query.toLowerCase()) !== -1; Writing it like this is a lot clearer. Furthermore it even returns `true` and `false` instead of some truthy/falsy integer.

kevincennis 14y ago

`indexOf` returns -1 if there's no match. Bitwise NOT on -1 will give you 0 -- for any other number, it'll return a truthy value. It's the same as: `return item.toLowerCase().indexOf(this.query.toLowerCase()) !== -1` If you're really dead set on doing things this way, it's safer to prefix with !! to coerce a real boolean: `return !!~item.toLowerCase().indexOf(this.query.toLowerCase())`