Skip to content

Instantly share code, notes, and snippets.

@bebraw
Created May 1, 2011 08:04
Show Gist options
  • Save bebraw/950339 to your computer and use it in GitHub Desktop.
Save bebraw/950339 to your computer and use it in GitHub Desktop.
Chaining assert statement for JavaScript
var assert = function(stmt) {
var methods = {
equals: {
error: function(val) {
return val + ' did not equal ' + stmt + '!'
},
method: function(val) {
return val == stmt;
}
},
is: {
error: function() {
// slow! http://bonsaiden.github.com/JavaScript-Garden/#function.arguments
var args = Array.prototype.slice.call(arguments);
if(args.length == 1) {
return stmt + ' is not a ' + args[0] + '!';
}
return stmt + ' not in types: ' + args.join(', ');
},
method: function() {
// borrowed from RightJS
var to_s = Object.prototype.toString;
var typeChecks = {
'function': function(val) {
return typeof(val) === 'function';
},
string: function(val) {
return typeof(val) === 'string';
},
number: function(val) {
return typeof(val) === 'number';
},
object: function(val) {
return to_s.call(val) === '[object Object]';
},
array: function(val) {
return to_s.call(val) === '[object Array]';
}
};
for(var i = 0; i < arguments.length; i++) {
var value = arguments[i];
if(value in typeChecks) {
var matched = typeChecks[value](stmt);
if(matched) {
return true;
}
}
}
return false;
}
},
isDefined: {
error: function() {
return 'Expected a defined value, got undefined instead!';
},
method: function() {
// borrowed from RightJS
return typeof(stmt) !== 'undefined';
}
},
between: {
error: function(a, b) {
return stmt + ' was not between ' + a + ' and ' + b + '!'
},
method: function(a, b) {
return a <= stmt && stmt <= b;
}
},
not: {
error: function() {},
method: function() {
invertNext = !invertNext;
return true;
}
}
};
var ret = {};
var invertNext = false;
var insertMethod = function(name, data) {
ret[name] = function() {
var success = data.method.apply(this, arguments);
if(name != 'not' && invertNext) {
success = !success;
invertNext = false;
}
if(success) {
return ret;
}
// http://aymanh.com/9-javascript-tips-you-may-not-know#assertion
function AssertionError(message) {
this.message = message;
}
AssertionError.prototype.toString = function () {
return 'AssertionError: ' + this.message;
}
var errorText = data.error.apply(this, arguments);
throw new AssertionError(errorText);
}
}
for(var methodName in methods) {
var methodData = methods[methodName];
insertMethod(methodName, methodData);
}
return ret;
}
var a = 5;
// these should pass
assert(a).equals(5);
assert(a).not().equals(10);
assert(a).not().not().equals(5);
assert(a).between(0, 10);
assert(a).isDefined();
assert(a).is('number');
assert(a).is('array', 'number');
// these should fail
assert(a).is('array', 'object');
assert(a).equals('foobar');
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment