src/mergeInto.js
function mergeInto(one, two) {
  checkMergeObjectArg(one);
  if (two != null) {
    checkMergeObjectArg(two);
    for (var key in two) {
      if (!two.hasOwnProperty(key)) {
        continue;
      }
      one[key] = two[key];
    }
  }
}
function mergeInto(one, two) {
  checkMergeObjectArg(one);
  if (two != null) {
    checkMergeObjectArg(two);
    for (var key in two) {
      if (!two.hasOwnProperty(key)) {
        continue;
      }
      one[key] = two[key];
    }
  }
}
function mergeInto ( one , two ) { checkMergeObjectArg ( one ) ; if ( two != null ) { checkMergeObjectArg ( two ) ; for ( var key in two ) { if ( ! two . hasOwnProperty ( key ) ) { continue ; } one [ key ] = two [ key ] ; } } }
Shallow merges two structures by mutating the first parameter.

@param {object} one Object to be merged into.
@param {?object} two Optional object with properties to merge from.
Shallow merges two structures by mutating the first parameter .