[Ref #15881] Use Explicit Values rather than Chain

[Ref #15881] Use Explicit Values for javascript variables rather than chained ones.

From https://github.com/twbs/bootstrap/pull/15881#discussion_r25330647

js/affix.js

@@ -21,8 +21,8 @@
       .on('click.bs.affix.data-api',  $.proxy(this.checkPositionWithEventLoop, this))
 
     this.$element     = $(element)
-    this.affixed      =
-    this.unpin        =
+    this.affixed      = null
+    this.unpin        = null
     this.pinnedOffset = null
 
     this.checkPosition()

js/carousel.js

@@ -17,10 +17,10 @@
     this.$element    = $(element)
     this.$indicators = this.$element.find('.carousel-indicators')
     this.options     = options
-    this.paused      =
-    this.sliding     =
-    this.interval    =
-    this.$active     =
+    this.paused      = null
+    this.sliding     = null
+    this.interval    = null
+    this.$active     = null
     this.$items      = null
 
     this.options.keyboard && this.$element.on('keydown.bs.carousel', $.proxy(this.keydown, this))

js/modal.js

@@ -17,7 +17,7 @@
     this.options        = options
     this.$body          = $(document.body)
     this.$element       = $(element)
-    this.$backdrop      =
+    this.$backdrop      = null
     this.isShown        = null
     this.scrollbarWidth = 0
 

js/tooltip.js

@@ -15,11 +15,11 @@
   // ===============================
 
   var Tooltip = function (element, options) {
-    this.type       =
-    this.options    =
-    this.enabled    =
-    this.timeout    =
-    this.hoverState =
+    this.type       = null
+    this.options    = null
+    this.enabled    = null
+    this.timeout    = null
+    this.hoverState = null
     this.$element   = null
 
     this.init('tooltip', element, options)