My collection of Underscore.js mixins

cm-mixins.js

_.mixin({
  
  // _.contains for strings with optional case sensitivity
  hasSubstring: function (stringA, stringB, caseSensitive) {
    if (caseSensitive) return stringA.indexOf(stringB) >= 0;
    return stringA.toLowerCase().indexOf(stringB.toLowerCase()) >= 0;
  },

  // Get the difference between two arrays - shallow only
  diffArrays: function (a, b) {
    // 1) Get the list of all unique values from both arrays (_.union)
    // 2) Reject any of the unique values that are present in both arrays (leaving the diff)
    return _(a).chain().union(b).reject(valueIsInBothArrays).value();

    function valueIsInBothArrays(value) {
      return _(a).indexOf(value) >= 0 && _(b).indexOf(value) >= 0;
    }
  },
  
  // Sum the numeric values of an array
  sum: function (arr) {
    return _(arr).reduce(function (sum, value) {
      return sum += value;
    }, 0);
  },
  
  // Just like _.tap, except returns the result of the interceptor instead of obj
  zap: function (obj, interceptor) {
    return interceptor(obj);
  },
  
  // Linear interpolation - t should be between 0 and 1
  lerp: function (t, min, max) {
    return min + (max - min) * t; 
  }

});