您需要转义引号,或使用double,或使用heredoc:
// Escaped
return \'<div id="xxxx-xxxxxx"></div>
<script type="text/javascript">
    window._taboola = window._taboola || [];
    _taboola.push({
        mode: \\\'xxxxxxx-xxxxx\\\',
        container: \\\'xxxxxx-xxxxxxx\\\',
        placement: \\\'one word word\\\',
        target_type: \\\'mix\\\'
    });
</script>\';
// Doubles
return \'<div id="xxxx-xxxxxx"></div>
<script type="text/javascript">
    window._taboola = window._taboola || [];
    _taboola.push({
        mode: "xxxxxxx-xxxxx",
        container: "xxxxxx-xxxxxxx",
        placement: "one word word",
        target_type: "mix"
    });
</script>\';
// Heredoc
return <<<html
<div id="xxxx-xxxxxx"></div>
<script type="text/javascript">
    window._taboola = window._taboola || [];
    _taboola.push({
        mode: "xxxxxxx-xxxxx",
        container: "xxxxxx-xxxxxxx",
        placement: "one word word",
        target_type: "mix"
    });
</script>
html;