js实现assert

String.prototype.subs = function(var_args) {
var ret = this;
for(var i = 0; i < arguments.length; i++) {
ret = ret.replace(/\%s/, String(arguments[i]));
}
return ret;
};

function assert(expr, m) {

var msg = "";

if(!expr){
if(isString(m)) {
msg = m;
}else if(isFunction(m)) {
msg = m();
}else {
msg = 'Assertion failed';
}

throw new MyException(msg);
}

}

function assertEqual(expected, actual, m) {
function generateMessage() {
var message = 'Expected: %s (%s), actual: %s (%s)'.subs(expected, typeof expected, actual, typeof actual);
return formatErrorMessage(message, m);
}

assert(expected == actual, generateMessage);
}

function assertNotEqual(unexpected, actual, m) {
function generateMessage() {
var message = 'Expected value other than "%s" (%s)'.subs(unexpected, typeof unexpected);
return formatErrorMessage(message, m);
}

assert(unexpected != actual, generateMessage);
}

function assertNull(val, m) {
assert(val === null, function() {
var message = "Expected null value.";
return formatErrorMessage(message, m);
});
}

function assertNotNull(val, m) {
assert(val !== null, function() {
var message = "Unexpected null value.";
return formatErrorMessage(message, m);
});
}

function MyException(message){
this.message = message;
}