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Handlers for Operators

Each method recognized in the handler for Proxy has a corresponding method with the same name in Reflect. Implementing such a Proxy method affects the corresponding Reflect method.

.get()

A trap for getting property values, eg. o[p], o.p.

.set()

A trap for setting property values, eg. o.p = X.


RESETRUNFULL
<!DOCTYPE html><html><body><script>

var handler = {
   get: function(target, prop, receiver) {
      return target[prop]*2;
   },
   set: function(target, prop, value, receiver) {
      target[prop]=value+100;
      return true;
   }};var o = {a:3};var p = new Proxy(o, handler);console.log(o.a);  // 3console.log(p.a);  // 6p.b = p.a;            // (changing p changes o)console.log(o.b);  // 106console.log(p.b);  // 212 ... (106*2)o.b = o.a;            // (changing o also changes p)console.log(o.b);  // 3console.log(p.b);  // 6 ... (3*2)var p = new Proxy(o,{        // (restore to default behaviours for these two handlers)
   get: Reflect.get,
   set: Reflect.set});p.b = p.a;console.log(p.b);  // 3

</script></body><html>

.has()

A trap for the in operator.


RESETRUNFULL
<!DOCTYPE html><html><body><script>

var p = new Proxy({}, {
   has: function(target, prop) {
      return true;
   }});console.log('a' in p);                 // trueconsole.log(Reflect.has(p,'a'));            // true
  … (affects the corresponding Reflect method)p = new Proxy({},Reflect);          // (restores all default behaviours)console.log('a' in p);                 // false

</script></body><html>

.deleteProperty()

A trap for the delete operator.


RESETRUNFULL
<!DOCTYPE html><html><body><script>

var p = new Proxy({a:3}, {
   deleteProperty: function(target, prop) {
      if (prop in target){
         delete target[prop];
         console.log('property removed: ' + prop);
         return true;
      } else {
         console.log('property not found: ' + prop);
         return false;
      }
   }});delete p.a;  // property removed: adelete p.a;  // property not found: a

</script></body><html>