类型错误：expect(...).not.toBe 不是函数

Question

Doing an exercise where I re-implement some functionality found in the Jasmine test framework. Specifically, I am running this line:

expect(false).not.toBe(true)

and I get a TypeError saying that toBe does not exist as a function. However, this line:

expect(true).toBe(true)

Passes. I suspect that it's an issue with my not() function returning this.

function ExpectedValue (val) {
    this.value = val;
    this.notted = false;

    this.not = function() {
        this.notted = !this.notted;
        return this;
    }

    this.toBe = function(b) {
        if (this.notted) {
            return this.value !== b;
        }
        else {
            return this.value === b;
        }
    }
}

function expect(a) {
    return new ExpectedValue(a);
}

console.log(expect(false).not.toBe(true));

Answer 1

Jasmine's not isn't a function. Yours is. But you're using it as though it were Jasmine's (without () ):

console.log(expect(false).not.toBe(true));
// Note no () ---------------^

Your not needs to be an object with all of the methods of the object you return from expect , but with their meaning inverted, eg:

 function ExpectedValue (val) { var self = this; self.value = val; this.not = { toBe: function(arg) { return !self.toBe(arg); } }; this.toBe = function(b) { return self.value === b; }; } function expect(a) { return new ExpectedValue(a); } console.log(expect(false).not.toBe(true));

There, it's manual, but that's not scaleable. Instead, you'd have an object with all of the methods on it, and create not by running through creating functions that invert the return.

arrayOfMethodNames.forEach(function(name) {
    target.not[name] = function() {
        return !target[name].apply(target, arguments);
    };
});