QWeb

The javascript QWeb implementation provides a few debugging hooks:

t-log

takes an expression parameter, evaluates the expression during rendering and logs its result with console.log:

<t t-set="foo" t-value="42"/>
<t t-log="foo"/>

will print 42 to the console

t-debug

triggers a debugger breakpoint during template rendering:

<t t-if="a_test">
    <t t-debug="">
</t>

will stop execution if debugging is active (exact condition depend on the browser and its development tools)

t-js

the node’s body is javascript code executed during template rendering. Takes a context parameter, which is the name under which the rendering context will be available in the t-js’s body:

<t t-set="foo" t-value="42"/>
<t t-js="ctx">
    console.log("Foo is", ctx.foo);
</t>

Source