enable dynamic el binding

Author: yyx990803

src/directives/el.js

@@ -6,19 +6,19 @@ module.exports = {
   priority: 1500,
 
   bind: function () {
-    var scope = this._scope || this.vm
-    var refs = scope.$$
-    var id = this.id = this.arg // bind-el ?
-      ? scope.$eval(this.expression)
-      : this.expression
-
-    if (process.env.NODE_ENV !== 'production' && this.arg) {
-      _.log(
-        'You are using bind- syntax on "el", which is a special ' +
-        'attribute. It will be evaluated only once.'
-      )
+    if (this.arg) {
+      this._isDynamicLiteral = true
+    } else {
+      this.update(this.expression)
     }
+  },
 
+  update: function (id) {
+    if (this.id) {
+      this.unbind()
+    }
+    this.id = id
+    var refs = (this._scope || this.vm).$$
     if (refs.hasOwnProperty(id)) {
       refs[id] = this.el
     } else {
@@ -27,6 +27,9 @@ module.exports = {
   },
 
   unbind: function () {
-    (this._scope || this.vm).$$[this.id] = null
+    var refs = (this._scope || this.vm).$$
+    if (refs[this.id] === this.el) {
+      refs[this.id] = null
+    }
   }
 }

test/unit/specs/directives/el_spec.js

@@ -43,7 +43,7 @@ if (_.inBrowser) {
       })
     })
 
-    it('bind-el', function () {
+    it('bind-el', function (done) {
       var vm = new Vue({
         el: el,
         data: {
@@ -53,7 +53,13 @@ if (_.inBrowser) {
       })
       expect(vm.$$.test).toBeTruthy()
       expect(vm.$$.test.id).toBe('test')
-      expect(_.log).toHaveBeenCalled()
+      vm.id = 'changed'
+      _.nextTick(function () {
+        expect(vm.$$.test).toBeNull()
+        expect(vm.$$.changed).toBeTruthy()
+        expect(vm.$$.changed.id).toBe('test')
+        done()
+      })
     })
 
     it('with v-repeat', function (done) {