title: javascript: left-merge two objects using EcmaScript 6 / immutable js
body: <p>I work in javascript Project.</p>
  
  <p>I'm now about search after option to merge two objects, as the second object will only ovveride fields of the first object and not add new fields which the second not has.</p>
  
  <p>Something like:</p>
  
  <pre><code>const firstObj = {name:'jon', age:'6}
  const secondObj = {name:'nir', mark:'100%'}
  
  const mergedObj = leftMerge(firstObj, secondObj);
  </code></pre>
  
  <p>So I like mergedObj to be:</p>
  
  <pre><code>{name:'nir', age:'6'}
  </code></pre>
  
  <p>Is I have any way to do that with javascript (I worl with EcmaScript 6), or with immutable.js library?</p>