What is the difference between these two applications of the && logical operator?

Question

What is the difference between these various uses of the && logical operator?

From the Oliver Steele Functional.js library. Line 4, "args.length & arg]:

0 Function.prototype.partial = function(){
1    var fn = this, args = Array.prototype.slice.call(arguments);
2    return function(){
3      var arg = 0;
4      for ( var i = 0; i < args.length && arg < arguments.length; i++ )
5        if ( args[i] === undefined )
6          args[i] = arguments[arg++];
7      return fn.apply(this, args);
8    };
9  };

From bootstrap.js . Line 11 below "," hover "& & this. $ Element":

1 var Carousel = function (element, options) {
2    this.$element    = $(element).on('keydown.bs.carousel', $.proxy(this.keydown, this))
3    this.$indicators = this.$element.find('.carousel-indicators')
4    this.options     = options
5    this.paused      =
6    this.sliding     =
7    this.interval    =
8    this.$active     =
9    this.$items      = null
10
11   this.options.pause == 'hover' && this.$element
12     .on('mouseenter.bs.carousel', $.proxy(this.pause, this))
13     .on('mouseleave.bs.carousel', $.proxy(this.cycle, this))
14 }

Also, why not just use the + arithmetic operator in the first example?

Here is another example that I have problems with grokking, from the same section of Carousel bootstrap.js:

this.options.interval
      && !this.paused
      && (this.interval = setInterval($.proxy(this.next, this), this.options.interval))

Answer 1

Well, this is the same operator all over the world, but the programmer uses it for different purposes.

args.length && arg, (i < args.length) && (arg < arguments.length), && , <. : " , i , arg ". , + .

, (&&) " ", , .. , .

, this.options.pause == 'hover' && this.$element.on(... - , "" ( , , , on ).

, setInterval ( this.interval), "true" ( , , undefined ...) .