{{#with}} Mustache helper pushes can.compute into Scope, breaks can.compute.read #871

bmomberger-reciprocity opened this Issue Apr 4, 2014 · 1 comment


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bmomberger-reciprocity commented Apr 4, 2014


I'm entirely unsure which function is in the wrong here, but here's the breakdown.

view/mustache/mustache.js, line 1996:

                'with': function(expr, options) {
                    var ctx = expr;
                    expr = Mustache.resolve(expr);
                    if ( !! expr) {
                        return options.fn(ctx);

expr is resolved and checked from ctx, as the result of executing ctx when ctx is a can.compute or a function. Then ctx (which may be a compute) is pushed onto the current Scope and the inner content of the {{#with}} block is run. If we try to then get attributes on the scope, there's an error thrown later.

Possible solution #1: options.fn(expr) instead of options.fn(ctx) -- this seems to be inline with https://github.com/wycats/handlebars.js/blob/master/spec/builtins.js which implies that the scope of a {{#with}} block includes the result of calling the function, not the function itself.

compute/compute.js, line 443, in can.compute.read:

        cur = cur.attr(reads[i]);

In the case of {{#with}}, cur starts out as a compute, and is not resolved, but prev is resolved to a can.Map, leading to this line of execution. cur does not have an attr function available; this is where the crash ultimately happens.

Possible solution #2: resolve cur if cur.isComputed at the beginning of can.compute.read

Doing both of the possible solutions is probably good for CYA against this happening again, but I'd like to hear from people who have worked on these modules.

@daffl daffl added this to the 2.3.0 milestone Oct 22, 2015


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daffl Oct 22, 2015


This is fixed in 2.3.0


daffl commented Oct 22, 2015

This is fixed in 2.3.0

@daffl daffl closed this Oct 22, 2015

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