Lodash _.templateSettings.imports

var compiled = _.template(
  '<% _.forEach(users, function(user) { %>' +
    '<li><%- user %></li>' +
  '<% }); %>'
);
compiled({ 'users': ['fred', 'barney'] });
// → '<li>fred</li><li>barney</li>'

// Official shape (needs jQuery on the page):
// var text = '<% jq.each(users, function(user) { %><li><%- user %></li><% }); %>';
// var compiled = _.template(text, { 'imports': { 'jq': jQuery } });

// Same idea with a tiny each helper:
var jq = {
  each: function (arr, fn) {
    for (var i = 0; i < arr.length; i++) fn(arr[i]);
  }
};
var text = '<% jq.each(users, function(user) { %><li><%- user %></li><% }); %>';
var compiled = _.template(text, { 'imports': { 'jq': jq } });
compiled({ 'users': ['fred', 'barney'] });
// → '<li>fred</li><li>barney</li>'

function shout(s) {
  return String(s).toUpperCase() + '!';
}
var compiled = _.template(
  'Hi <%- shout(name) %>',
  { imports: { shout: shout } }
);
compiled({ name: 'ada' });
// → 'Hi ADA!'

var compiled = _.template(
  'max=<%= _.max(scores) %>'
);
compiled({ scores: [3, 9, 4] });
// → 'max=9'

_.keys(_.templateSettings.imports);
// → ['_']   (typical full build)

typeof _.templateSettings.imports._;
// → 'function'