JSLint: Unexpected assignment expression

问题

I get this warning:

Unexpected assignment expression.
return task.completed = true; // Line 63, Pos 39

When using this code:

completeAll: function () {
    this.tasks = this.tasks.filter(function (task) {
        return task.completed = true;
    });
}

Why? And how else could I write this expression to avoid JSLint throwing warnings?

P.S.

The codeblock is taken from the Vue TodoMVC Example here: http://todomvc.dev/examples/vue/, therefore I assume that code review must have already been happened.

回答1:

It's doing that because it's warning you that you're using = rather than == or === in a context where you're not just assigning, but also doing something with the assigned result. That's perfectly valid JavaScript, but it's frequently unintentional. A better example is:

if (foo = bar) {
    // ...
}

...where you probably meant == or === (checking that they were equal).

How you fix it depends on what you're trying to do. From the name of the method, I assume you're (well, they're) trying to set task.completed, in which case frankly filter is the wrong function to use; they should be using forEach:

completeAll: function () {
    this.tasks.forEach(function (task) {
        task.completed = true;
    });
}

but if you (they) really wanted to use filter:

completeAll: function () {
    this.tasks = this.tasks.filter(function (task) {
        task.completed = true;
        return true; // Or return task.completed
    });
}

If you're trying to do a comparison (which I doubt), not an assignment, then:

return task.completed == true;

return !!task.completed;

return task.completed; // If you know it's boolean already

来源：https://stackoverflow.com/questions/32474106/jslint-unexpected-assignment-expression

标签

javascript

Vue.js

jslint