Fix #84 : Add a more friendly way to update a single parameter on Sea…

…rchParameters

src/SearchParameters/index.js

@@ -706,13 +706,32 @@ SearchParameters.prototype = {
     return Object.freeze( newState );
   },
   /**
-   * Function that let the user set any of the parameters with a plain object.
+   * Let the user set a specific value for a given parameter. Will return the
+   * same instance if the parameter is invalid or if the value is the same as the
+   * previous one.
+   * @method
+   * @param {string} parameter the parameter name
+   * @param {any} value the value to be set, must be compliant with the definition of the attribute on the object
+   * @return {SearchParameters} the updated state
+   */
+  setQueryParameter : function setParameter( parameter, value ) {
+    var k = keys( this );
+    if( k.indexOf( parameter ) === -1 ) return this;
+    if( this[ parameter ] === value ) return this;
+
+    return this.mutateMe( function updateParameter( newState ) {
+      newState[ parameter ] = value;
+      return newState;
+    } );
+  },
+  /**
+   * Let the user set any of the parameters with a plain object.
    * It won't let the user define custom properties.
    * @method
    * @param {object} params all the keys and the values to be updated
    * @return {SearchParameters} a new updated instance
    */
-  setQueryParameters : function setQueryParams( params ) {
+  setQueryParameters : function setQueryParameters( params ) {
     return this.mutateMe( function merge( newInstance ) {
       var ks = keys( newInstance );
       forEach( ks, function( k ) {

test/spec/SearchParameters.setQueryParameter.js

@@ -0,0 +1,57 @@
+"use strict";
+var test = require( "tape" );
+//var _ = require( "lodash" );
+var SearchParameters = require( "../../src/SearchParameters" );
+
+test( "setqueryparameter should update existing parameter", function( t ) {
+  var sp = new SearchParameters( {
+    facets : ["facet"]
+  } );
+
+  var newValue = [];
+  var newsp = sp.setQueryParameter( "facets", newValue );
+
+  t.equal( newsp.facets, newValue, "update of an existing parameter" );
+
+  t.end();
+} );
+
+test( "setqueryparameter should add non-existing parameter", function( t ) {
+  var sp = new SearchParameters( {
+    facets : ["facet"]
+  } );
+
+  var newValue = [ "attributesToHighlight" ];
+  var newsp = sp.setQueryParameter( "attributesToHighlight", newValue );
+
+  t.equal( newsp.attributesToHighlight, newValue, "add new parameter" );
+
+  t.end();
+} );
+
+test( "setQueryParameter should not create a new instance if the update is non effective", function( t ) {
+  var sp = new SearchParameters( {
+    facets : ["facet"],
+    maxValuesPerFacet : 10
+  } );
+
+  var newValue = 10;
+  var newsp = sp.setQueryParameter( "maxValuesPerFacet", newValue );
+
+  t.equal( newsp, sp, "No change should result in the same instance" );
+
+  t.end();
+} );
+
+test( "setQueryParameter should not create a new instance if the parameter is unknown", function( t ) {
+  var sp = new SearchParameters( {
+    facets : ["facet"]
+  } );
+
+  var newValue = [ "attributesToHighlight" ];
+  var newsp = sp.setQueryParameter( "unknown", newValue );
+
+  t.equal( newsp, sp, "Unknown parameter should return the same instance" );
+
+  t.end();
+} );